Nuclear waste cask with impact protection, impact amelioration system for nuclear fuel storage, unventilated cask for storing nuclear waste, and storage and transport cask for nuclear waste

ABSTRACT

A nuclear waste cask with impact protection includes impact limiters comprising deformable energy-absorbing perforated sleeves. An impact amelioration system for nuclear fuel storage components includes impact limiter assemblies at the bottom cask to canister interface including impact limiter plugs frictionally engaging corresponding plug holes formed in the cask closure plate. A nuclear waste fuel storage system includes an unventilated cask including a heavy free-floating radiation shielding lid loosely coupled the top end of the cask in a movable manner via the anchor bosses which provides cask overpressurization protection. A nuclear waste cask includes an axially elongated rectangular cuboid cask body having a cavity for holding nuclear waste materials and cask locking mechanism including first locking protrusions on the lid which are selectively interlockable with mating second locking protrusions on the cask body to lock the lid to the cask body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 17/061,700 filed Oct. 2, 2020, which claims the benefit of U.S.Provisional Application No. 62/910,073 filed Oct. 3, 2019; which areeach incorporated herein by reference in their entireties.

This application is a continuation-in-part of U.S. patent applicationSer. No. 17/132,102 filed Dec. 23, 2020, which claims the benefit ofU.S. Provisional Application No. 62/954,083 filed Dec. 27, 2019; whichare each incorporated herein by reference in their entireties.

This application is a continuation-in-part of U.S. patent applicationSer. No. 17/165,224 filed Feb. 2, 2021, which claims the benefit of U.S.Provisional Application No. 62/969,183 filed Feb. 3, 2020; which areeach incorporated herein by reference in their entireties.

This application is a continuation-in-part of U.S. patent applicationSer. No. 17/181,439 filed Feb. 22, 2021, which claims the benefit ofU.S. Provisional Application No. 62/979,640 filed Feb. 21, 2020; whichare each incorporated herein by reference in their entireties.

BACKGROUND

The present invention in one aspect relates generally to systems andapparatuses for storing high level radioactive waste such as used orspent nuclear fuel, and more particularly to an improved nuclear fuelcask with impact protection.

In the operation of nuclear reactors, the nuclear energy source is inthe form of hollow zircaloy tubes filled with enriched uranium,collectively arranged in multiple assemblages referred to as fuelassemblies. When the energy in the fuel assembly has been depleted to acertain predetermined level, the used or “spent” nuclear fuel (SNF)assemblies are removed from the nuclear reactor. The standard structureused to package used or spent fuel assemblies discharged from lightwater reactors for off-site shipment or on-site dry storage is known asthe fuel basket. The fuel basket is essentially an assemblage ofprismatic storage cells each of which is sized to store one fuelassembly that comprises a plurality of individual spent nuclear fuelrods. The fuel basket is arranged inside a cylindrical metallic storagecanister (typically stainless steel), which is often referred to as amulti-purpose canister (MPC), which forms the primary nuclear wastecontainment barrier. The fuel assemblies are typically loaded into thecanister while submerged in the spent fuel pool of the reactorcontainment structure to minimize radiation exposure to personnel. Thecanisters which typically comprise a single metal shell have limitedability however to block or attenuate the gamma and neutron radiationemitted by the decaying SNF other than borated water remaining in thecanister from the spent fuel pool.

To transport the nuclear waste canister loaded with SNF or other waste,the canister is placed into a radiation-shielded outer ventilatedoverpack or cask for safe transport and storage of the waste. The caskforms the secondary containment barrier. Casks are used to transfer theSNF or other high level nuclear waste from the spent fuel pool (e.g.“transfer cask”) in the nuclear reactor containment structure to a moreremote interim term storage such as in the dry cask storage system of anon-site or off-site independent spent fuel storage installation (ISFSI)until a final repository for spent nuclear fuel is available from thefederal government.

A typical modern transport cask, used to move radiative nuclear waste,including spent nuclear fuel, is a heavy cylindrical weldmenttransported over railroads or occasionally by sea on ships. A typicaltransport cask may be equipped with an impact limiter of some form ateach extremity. The external diameter of such cask package is governedby the narrowest passage through which the rail car carrying the loadedcask must pass. Typically, the narrowest passageway in the caskpackage's travel path is a tunnel, or sometimes a low-profile bridgeunderpass. Since casks are extremely tall structures, the casks aretypically transported in a horizontal position on the rail car. In theUS, the outside diameter (OD) of the impact limiter is limited to 128inches to avoid clearance issues in tunnels. In most other countries, itis even smaller.

Impact limiters are fabricated from energy-absorbing materials thatprevent or limit structural damage to the transport cask in case of anaccident to prevent release of radiation to the environment. Suchdevices are mandate by the NRC (Nuclear Regulatory Commission) fornuclear waste transport packages such as casks and must undergo droptests to evaluate their effectiveness. In the past, plastic foams, metalhoneycombs, and wood have been used. Impact limiters made of organicmaterials such as wood have many drawbacks. Wood is inherentlynon-homogeneous and non-isotropic, its strength properties are affectedby weather, and it is flammable. Therefore, the main appeal of woodimpact limiter is low cost. The standard honeycomb impact limiter ismade by placing alternate layers of solid corrugated aluminum sheets orpanels 10 laid out in alternating orthogonal directions to each otherand bonding the layers together by a high-temperature epoxy (see, e.g.FIG. 29 ). The layers are cut to a circular or other shape and stackedon top of each other being oriented transversely to longitudinal axis ofthe cask such that there are no openings between the layers extend inthe longitudinal direction of the cask. Honeycomb impact limiters aretypically time intensive and expensive to manufacture, and in generallyscare supply.

Accordingly, there remains a need for improvements in impact limitersfor nuclear waste transport casks.

The present invention in another aspect relates generally to systems andvessels for storing high level radioactive waste such as used or spentnuclear fuel (SNF), and more particularly to an improved system whichameliorates the effects of a forceful impact on such nuclear fuelstorage vessels and concomitantly the SNF assemblies stored therein.

In the operation of nuclear reactors, the nuclear energy source is inthe form of hollow Zircaloy tubes filled with enriched uranium,collectively arranged in multiple assemblages referred to as fuelassemblies. When the energy in the fuel assembly has been depleted to acertain predetermined level, the used or “spent” nuclear fuel (SNF)assemblies are removed from the nuclear reactor. The standard structureused to package used or spent fuel assemblies discharged from lightwater reactors for off-site shipment or on-site dry storage is known asthe fuel basket. The fuel basket is essentially an assemblage ofprismatic storage cells each of which is sized to store one fuelassembly that comprises a plurality of individual spent nuclear fuelrods. The fuel basket is arranged inside a cylindrical metallic fuelstorage canister, which is often referred to as a multi-purpose canister(MPC) that forms the primary nuclear waste containment barrier. SuchMPCs are available from Holtec International of Camden, N.J. The fuelassemblies are typically loaded into the canister while submerged in thespent fuel pool of the reactor containment structure to minimizeradiation exposure to personnel.

The fuel canister loaded with SNF (or other high level radioactivewaste) is then placed into an outer overpack or cask, which forms thesecondary containment, for safe transport and storage of the multiplespent fuel assemblies. Casks are heavy radiation shielded containersused to store and/or transfer the SNF canister from the spent fuel pool(“transfer cask”) in the nuclear reactor containment structure to a moreremote staging area for interim term storage such as in the dry caskstorage system of an on-site or off-site independent spent fuel storageinstallation (ISFSI) until a final repository for spent nuclear fuel isavailable from the federal government.

Drop events involving heavy loads such as nuclear waste fuel casks areamong the more serious accidents in industry. In the nuclear industry,an accidental drop of a cask onto a stationary reinforced concretesurface is a typical postulated scenario involving a hard and heavyobject slamming onto a highly inflexible surface. Classical dynamicsteaches us that the deceleration g-load under such an impact scenario isroughly proportional to the square root of the stiffness of theimpacting interface. The more rigid the impactor and the stationarytarget, the higher is the g-load. Reducing the g-load is essential tominimize the physical damage to the colliding bodies; which iscritically important if one of the two bodies contains a hazardousradioactive material such as spent nuclear fuel.

Accordingly, there remains a need for improvements in controlling andreducing the g-load associated with impacts occurring with the foregoingnuclear waste storage systems.

The present invention in another aspect relates generally to systems andvessels for storing high level radioactive nuclear waste such as used orspent nuclear fuel (SNF), and more particularly to an improvedunventilated storage cask system for storing nuclear waste.

In the operation of nuclear reactors, the nuclear energy source is inthe form of hollow Zircaloy tubes filled with enriched uranium,collectively arranged in multiple assemblages referred to as fuelassemblies. When the energy in the fuel assembly has been depleted to acertain predetermined level, the used or “spent” nuclear fuel (SNF)assemblies are removed from the nuclear reactor. The standard structureused to package used or spent fuel assemblies discharged from lightwater reactors for off-site shipment or on-site dry storage is known asthe fuel basket. The fuel basket is essentially an assemblage ofprismatic storage cells each of which is sized to store one fuelassembly that comprises a plurality of individual spent nuclear fuelrods.

The fuel basket is arranged inside a cylindrical metallic nuclear wastefuel canister, which is often referred to as a multi-purpose canister(MPC). Such MPCs are available from Holtec International of Camden, N.J.The fuel assemblies are typically loaded into the canister whilesubmerged in the spent fuel pool of the reactor containment structure tominimize radiation exposure to personnel.

An essential attribute of such a fuel storage MPC is that it is designedand manufactured to provide safe radiological confinement to itscontents and satisfies the criterion of “leak tight” (againstparticulate and gaseous radiological matter) as defined in the USNRCregulatory guidance documents. Such a waste package, however, is notautonomously capable of providing protection against neutrons and gammaradiation emanating from its contents which would, if exposed tobiological life would be deadly. Therefore, the MPC needs to be storedin a heavily radiation-shielded outer cask that permits as littleradiation as possible to escape to the environment. The storage caskmust also be able to transmit and dissipate the decay heat generatedinside the MPC by the decaying fuel assemblies to the ambientenvironment. Effective heat rejection and effective reduction ofradiation are thus the twin functions of the storage cask, also referredto in the industry as an “overpack” or “storage module.”

The storage cask used to store the loaded canister has historically beenin the form of a ventilated cask wherein ambient ventilation air entersthe cask near the bottom and exits near the top thereby convectivelyremoving heat emitted by the canister. Ventilated cask designs arewidely used for storing nuclear waste fuel canisters with aggregate heatloads as high as 50 kW. However, such ventilated cask suffer from onepotential vulnerability in marine environments where the salt-ladenambient ventilation air can induce stress corrosion cracking (SCC) inthe canister's austenitic stainless-steel confinement boundary. SCC is awell-documented problem encountered in the nuclear fuel storageindustry. Ventilated overpacks also need to be surveilled regularly toensure that their vent passages are not blocked which an diminish heatrejection from the cask.

Accordingly, there remains a need for an improved nuclear waste storagecask that provides the necessary heat dissipation and radiation blockagefunctions, but eliminates the risk of initiating stress corrosioncracking on the exterior surfaces of the waste fuel canister inside thecask.

The present invention in another aspect relates generally to systems andvessels for transporting and storing high level radioactive nuclearwaste materials, and more particularly to a box-type cask in oneembodiment for transport and storage of radioactive nuclear wastematerials.

The overpacks or casks used to store neutron activated metal and otherradiated non-fissile high level radioactive waste, such as thatresulting from operation nuclear power generation plants or other typefacilities, is typically an open-top cylindrical structure with a boltedcircular lid. Such a cask is inefficient to load all types of nuclearwaste materials not limited to spent nuclear fuel into the cask. Theradiation waste materials are often too large and/or may be irregularshaped for insertion through the narrow top access opening in suchcylindrical casks which leads to the internal storage cavity. Further,the act of tightening the bolts once the cylindrical cask is packed withnuclear waste materials is a time consuming which exposes the workers toradiation dosage in proportion to the time needed to complete thetedious installation of the closure bolts.

Accordingly, there remains a need for an improved nuclear waste storagecask that can accommodate a wide variety of waste materials, and whichcan further be closed and sealed in an expedient manner to reduceradiation exposure of operating personnel handling the cask.

BRIEF SUMMARY

A First Inventive Concept of the present application discloses a nuclearwaste transport cask with improved impact protection provided by impactlimiters which are economical to manufacture and overcome the drawbacksof the foregoing prior impact limiter designs. The present impactlimiters comprise cylindrical structures which are detachably coupled tothe top and bottom extremities of the cask. Each impact limiter maycomprise a deformable and crushable annular metallic perforated impactbarrel or sleeve of cylindrical shape comprising a plurality ofelongated perforations in the form of longitudinal passages. Thepassages may have a circular cross-sectional shape in certainembodiments. The perforated sleeve has an annular metallic body ofmonolithic unitary structure in which the perforations are formed and anenlarged central opening to receive the ends of the cask therein.

The longitudinal passages of the perforated sleeve form open passagewayswhich extend between opposite ends of the sleeve in a direction parallelto each other, and in one embodiment parallel to the longitudinal axisof the vertically elongated transport cask. The passages defineligaments or webs of solid material between adjacent perforations. Whenthe impact limiters are subjected to an inward-acting external impactforce having a radial component (e.g. perpendicular or obliquely angledtransversely to the longitudinal axis of the cask) caused by droppingthe cask horizontally on its side or end first at an angled orientationto horizontal, the perforations radially collapse in the impact or crushzone. The outer webs in the impact zone increasingly deform inwardlyunder the impact while collapsing the perforations, and may contact atleast some of the more inner webs in the crush zone which slows theprogression of deformation and collapse of the impact ring is resistedby the solid web material. The amount of deformation experienced byperforation sleeve or ring is generally the result of the magnitude ofthe external impact force, diameter of perforations, pitch or spacingbetween the perforations, diameter of the perforations and webthickness, and modulus of elasticity of metal selected for the impactrings. In one example, the impact rings may be formed of a softisotropic material such as without limitation a suitable grade or alloyof aluminum; however, other suitable metallic materials may be used.

According to one aspect, a nuclear waste cask with impact protectioncomprises: a longitudinal axis; a longitudinally elongated cask bodyincluding a top end, a bottom end, a sidewall extending between theends, and a cavity configured for holding a nuclear waste canister; andan impact limiter coupled to the top end of the cask body, the impactlimiter comprising an annular perforated sleeve having a body includinga central opening and a circumferential array of elongated longitudinalpassages formed therethrough around the central opening. The body of theperforated sleeve may be formed of a solid metal ring of monolithicunitary structure. The longitudinal passages may be oriented parallel toeach other and the longitudinal axis of the cask in one embodiment.

According to another aspect, a nuclear waste cask with impact protectioncomprises: a longitudinal axis; a longitudinally elongated caskincluding a top end, a bottom end, a sidewall extending between theends, and a cavity configured for holding a nuclear waste canister; andan impact limiter coupled to each of the top and bottom ends of thecask; the impact limiter comprising an outer shell and an innerperforated core of monolithic unitary structure. In one embodiment, theperforated core comprises an annular sleeve including a plurality ofelongated longitudinal passages oriented parallel to the longitudinalaxis of the cask.

A Second Inventive Concept of the present application discloses animpact amelioration or limiting system usable in nuclear waste fuelstorage vessels. The system operates to ameliorate and reduce the g-loador force (gravitational) imparted to such vessels due to mutual impactbetween the vessels resulting from a drop event. The proposed impactlimiting system design can comprise installing one or preferably moretapered impact limiter rods or plugs in closely fitting and frictionallyengaged tapered plug holes formed in one of the two mutually impactingvessels. The combination tapered plug and corresponding holecollectively defines an impact limiter assembly. In one embodiment, theimpacting vessels may be without limitation an outer nuclear wastetransfer overpack or cask and a SNF storage canister (aka fuel canister)such as a MPC described above. The impact limiter rods or plugs andcorresponding tapered plug holes may be arranged on the cask in oneconfiguration at the interface between the bottom of the canister andbottom closure plate of the cask. The impact amelioration system isdesigned to absorb and dissipate at least a portion of the kineticenergy imparted to the vessels during a cask drop event, as furtherdescribed herein.

The impact limiter plugs are partially embedded in their respective plugholes. Under impact during a generally vertical drop scenario, eachtapered impact limiter plug that may be provided when acted upon by thecanister will advance a distance deeper inside its respective taperedhole in the cask. The impact force of the plug's kinetic energy isabsorbed by the combined action of interfacial friction (between engagedside surfaces of the plug and hole walls) and the elastic-plastic(elastoplastic) deformation and expansion of the plugs within thetapered holes. Accordingly, the partially embedded plugs which protrudeabove top surface of the bottom closure plate of the cask are drivendeeper into the plug holes by the impact force. Calculations show that asuitable choice of the principal parameters such as the material of thetapered rod, angle of taper, rod diameter, and number of impact limiterrods or plugs provided results in reducing the peak g-load resultingfrom the impact significantly. Advantageously, this protects andminimizes or prevents the spent nuclear fuel (SNF) assemblies storedwithin the fuel canister from damage during the impact scenario.

A plurality of impact limiter rod or plugs and corresponding taperedplug holes may be arrayed around and partially embedded in the topsurface of the bottom closure plate of the cask. The plugs protrudeupwards beyond the top surface towards the canister in a patternselected to provide impact protection in a uniform manner at the bottomor lower cask to canister interface. The canister is seated on the topsurfaces of the plugs which act as pedestals that support the canisterin a spaced apart manner from the cask bottom closure plate. Thecanister therefore does not directly contact the bottom closure plate ofthe cask. All quadrants of the cask bottom closure plate may include atleast one impact limiter assembly (i.e. tapered plug and hole), butpreferably multiple impact limiter assemblies. This ensures evendistribution of the impact forces in the event of a generally straightvertical drop and/or guarantees that an off-center drop at an angle willresult in at least some impact limiter assemblies being positioned toabsorb the resultant impact forces and decelerate the canister to reducepeak g-loads.

An impact amelioration system for nuclear fuel storage components in oneembodiment comprises: a fuel storage canister comprising a first shellextending along a vertical centerline, the canister configured forstoring nuclear fuel; an outer cask defining a cavity receiving thecanister, the cask comprising a second shell and a bottom closure plateattached to the second shell; a plurality of impact limiter assembliesdisposed on the bottom closure plate at a canister to cask interface,each of the impact limiter assemblies comprising a plug frictionallyengaged with a corresponding plug hole formed in the bottom closureplate; wherein the plugs engage the canister.

A method for ameliorating impact between components of a fuel storagesystem in one embodiment comprises: partially embedding a plurality ofimpact limiter plugs in corresponding plug holes formed in a bottomclosure plate of a cask; seating the canister on the plugs, the plugsbeing positioned at a first depth in the plug holes; impacting thecanister against the plugs with an impact force; and driving the plugsto a second depth in the plug holes deeper than the first depth.

A Third Inventive Concept of the present application discloses aradiation-shielded unventilated nuclear waste storage cask with heatdissipation system which effectively removes decay heat emitted from thenuclear waste fuel canister housed therein. In one embodiment, the caskcomprises an inner shell, outer shell, and plurality of radial ribplates connected between the shells which convey heat away from thecanister through the walls of the cask to the ambient environment. Theouter shell is cooled by convection via ambient airflow and radiationeffects. Radiation shielding is provided in the annulus between theshells and the rib plate therein. The rib plates further structurallyreinforced the cask and play a role in lifting the cask, as furtherdescribed herein.

In contrast to the typical ventilated storage casks discussed above, thepresent unventilated storage cask is hermetically sealed forming apressure retention vessel configured to contain pressures in excess ofatmospheric pressure. Because there is no ambient air exchanged with thesealed internal cavity of the unventilated storage cask in which thewaste fuel canister is stored, the risk of initiating stress corrosioncracking (SCC) of the canister is effectively mitigated. Theunventilated storage cask also includes a safety feature comprising apressure relief mechanism to relieve the buildup of excessive pressurewithin the pressure vessel class cask. Excess pressure is safelyreleased to atmosphere by a unique floating lid to cask interface designwhich protects the structural integrity of the unventilated cask andwaste fuel canister therein. When overpressurization conditions abate,the lid automatically reseals the cask cavity.

As its design configuration indicates, the unventilated storage cask hasa considerably reduced heat load capacity compared to its ventilatedcounterpart. Because the only heat rejection pathway available in thepresent unventilated storage system is via conduction through the shellsof the cask and natural convection/radiation at the cask's exteriorsurface to the ambient, the annulus gas inside the overpack will be atan elevated temperature. Because heating of air reduces its relativehumidity and a high humidity content is necessary (but not sufficient)to induce stress corrosion cracking (SCC) in the austenitic stainlesssteel confinement boundary of the waste fuel canister, increasing thetemperature of the air surrounding the canister in the internal cavityof the cask serves to prevent the onset of SCC under extended storageconditions. A preferred alternative is to replace the air within theannular area of the cask surrounding the canister with a non-reactivegas, such for example without limitation as nitrogen or argon.Preventing SCC in long term dry storage casks of the present design isone objective of the present unventilated nuclear waste fuel storagesystem.

If SCC is not a major threat in the nuclear waste fuel storageenvironment, then it is not necessary to purge the ambient air from thecask for replacement with an inert gas. In such a case, the air pressurein the hermetically sealed cavity of the unventilated storage cask willrise in temperature roughly in accordance with the perfect gas law. Toprovide pressure relief under a U.S. NRC (Nuclear Regulatory Commission)postulated accident scenario to which dry cask waste fuel storagesystems must be designed, such as the cask's Design Basis Fire Event,the cask closure lid bolt assemblies are installed with a small verticalgap to loosely mount the lid to the cask body with a copious presetvertical travel clearance or gap to enable the lid to slideably lift upwithout frictional interference from the bolts. If the air pressurewithin the cask is high enough to lift the lid even by a minute amount,then some air will escape reducing the pressure within the cask back tonormal operating pressures. Thus, the cask is a self-regulating andself-relieving device making uncontrolled overpressure impossible, asfurther described herein. In some embodiments, the internal designpressure of the cask may be set equal to approximately 200% of thepressure that will equilibrate the weight of the cask closure lid.

In one aspect, an unventilated nuclear waste fuel storage systemcomprises: a longitudinal axis; a canister configured for storingnuclear waste fuel inside; an outer cask comprising a cask bodyincluding an inner shell, an outer shell, an annular space containing aradiation shielding material formed between the shells, and a bottombaseplate sealed to bottom ends of the shells; a radiation shielding lidselectively sealable to the cask body, the lid when positioned on thecask body collectively defining a gas tight cavity receiving thecanister; a plurality of longitudinal lifting rib plates extendingradially between and fixedly attached to the inner and outer shells inthe annular space, each lifting rib plate comprising a threaded anchorboss fixedly attached at a top end thereof; and a plurality of threadedbolt assemblies threadably engaged with the anchor bosses which securethe lid to the cask; wherein the gas tight cavity forms a pressurevessel operable to retain pressures above atmospheric pressure withinthe cask.

According to another aspect, an unventilated nuclear waste fuel storagepressure vessel with self-regulating internal pressure relief mechanismcomprises: a longitudinal axis; a cask body including an inner shell, anouter shell, an annular space containing a radiation shielding materialformed between the shells, a bottom baseplate sealed to bottom ends ofthe shells, and an internal cavity configured to house a nuclear wastefuel canister therein; a plurality of upwardly open threaded anchorbosses affixed to a top end of the cask body; a radiation shielding lidloosely coupled to the top end of the cask body in a movable manner; anannular compressible gasket forming a circumferential seal between thelid and the top end of the cask body which renders the cavity gas tight;and a plurality of bolt assemblies passing through the lid andthreadably engaged with the anchor bosses, the bolt assembliesconfigured and operable to loosely secure the lid to the cask body; thelid being movable between (1) a downward sealed position engaged withthe cask body which seals the gas tight cavity of the cask; and (2) anadjustable raised relief position engaged with the bolt assemblies butajar from the top end of the cask body to partially open the gas tightcavity thereby defining a gas overpressurization relief passageway toambient atmosphere; wherein the cask is operable to retain an internalpressure within the cavity above atmospheric pressure.

According to another aspect, a method for protecting an unventilatednuclear waste storage system from internal overpressurization comprises:providing an unventilated cask comprising a sealable internal cavity anda plurality of threaded anchor bosses; lowering a canister containinghigh level nuclear waste into the cavity; positioning a radiationshielded lid on the cask, the lid being in a downward sealed positionengaged with the cask making the cavity gas tight to retain pressuresexceeding atmospheric; aligning a plurality of fastener holes formed inthe lid with the anchor bosses; threadably engaging a threaded stud witheach of the anchor bosses through the fastener holes of the lid;rotatably engaging a threaded limit stop with each of the threadedstuds; positioning the limits stops on the studs such that a verticaltravel gap is formed between the lid and the limit stops; wherein duringa cask overpressurization condition, the lid slideably moves upwardalong the studs to a relief position ajar from the cask to vent excesspressure to atmosphere.

A Fourth Inventive Concept of the present application provides a nuclearwaste storage system comprising a radiation-shielded nuclear wastestorage cask which overcomes the shortcomings of the foregoingcylindrical type storage casks described above for storing a widevariety of different nuclear waste materials. In one embodiment, alongitudinally elongated box-type cask is disclosed comprising anessentially rectangular body with rectilinear cross sectional internalstorage cavity configured for holding nuclear waste material, and amatching rectangular closure lid. The elongated large top openingleading into the storage cavity extends for a majority of thelongitudinal length of the cask. In contrast to the small circularopening at the top of cylindrical casks, the present rectangular openingallows large and irregular shaped radioactive metal pieces of wastematerial to be loaded inside the cask storage cavity in an efficient andexpedient manner without undue handling by operating personnel, therebyreducing potential radiation dosage.

In one embodiment, the closure lid be coupled and sealed to the caskbody to close the top opening through a quick connect-disconnect jointthat does not utilize any threaded fasteners. Instead, a slider lockingmechanism comprising mechanically interlocking protrusions provided onperipheral portions of each of the lid and correspondingly cask bodyaround the cask top opening is employed. While the lid remainsstationary on the cask body, the locking protrusions on the lid areslideably relative to the locking protrusions on the cask body betweenlocked and unlocked positions or states. The locking protrusions may bearrayed and spaced apart perimetrically around the lid and cask body.The locking protrusions may be wedge-shaped in one embodiment to producea wedging-action when mutually engaged which effectively locks the lidto the cask body and seals the nuclear waste contents inside the cask. Agasket at the lid to cask body interface is compressed by thewedging-action to form a gas-tight seal of the cask storage cavity whichcompletes the containment barrier. There is no exchange of air betweenthe ambient environment and the storage cavity in one embodiment.

The term “nuclear waste material” as used herein shall be broadlyconstrued to mean any type or form of radioactive waste material whichhas been irradiated by a source of radiation. Such irradiation may occurin a nuclear power generation plant with nuclear reactor, or other typesof facilities. As one non-limiting example, the radioactive nuclearwaste materials may be associated with decommissioning orrepair/maintenance of a nuclear facility, and may therefore include awide variety of sizes and shapes of pieces of equipment (including partsof the reactor), structural components/members, parts, debris, scrap, orsimilar which have been irradiated and generate radiation.

In one aspect, a cask for containing radioactive materials comprises: acask body comprising an opening forming a passageway into an internalstorage cavity of the cask; a closure lid configured to be detachablycoupled to the cask body to enclose the opening; and a locking mechanismcomprising at least one first locking member and at least one secondlocking member, the first and second locking members slideable relativeto one another to alter the locking mechanism between: (1) a first statein which the closure lid can be removed from the cask body; and (2) asecond state in which the first and second locking members engage oneanother to prevent the closure lid from being removed from the caskbody.

According to another aspect, a cask for containing radioactive materialscomprises: a longitudinal axis; an axially elongated cask body defininga top opening forming an entrance to an internal storage cavity ofnon-cylindrical cross-sectional configuration, the cavity configured forholding radioactive waste materials; and a closure lid detachablycoupled to the cask body at the top opening.

According to another aspect, a method for locking a radioactive wastestorage cask comprises: positioning a closure lid on a cask body over anopening leading into an internal storage cavity; inserting a peripheralarray of first locking protrusions on the lid between and through aperipheral array of second locking protrusions disposed on the cask bodyaround the opening; slideably moving the first locking protrusionsbeneath the second locking protrusions; and frictionally engaging thefirst locking protrusions with the second locking protrusions; whereinthe lid cannot be removed from the cask body.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the exemplary (“example”) embodiments of the invention, areintended for purposes of illustration only and are not intended to limitthe scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein likeelements are labeled similarly and in which:

FIG. 1 is a top perspective view of a nuclear waste cask for storinghigh level radioactive materials with mounted impact limiters accordingto the present disclosure;

FIG. 2 is a second top perspective view thereof;

FIG. 3 is a first side view thereof;

FIG. 4 is a second side view thereof;

FIG. 5 is a top view thereof;

FIG. 6 is a bottom view thereof;

FIG. 7 is a longitudinal cross-sectional perspective view thereof;

FIG. 8 is a first side cross-sectional view thereof;

FIG. 9 is a second side cross-sectional view thereof;

FIG. 10 is an enlarged top detail taken from FIG. 9 ;

FIG. 11 is an enlarged bottom detail taken from FIG. 9 ;

FIG. 12 is an exploded side view of the cask and impact limiters of FIG.1 ;

FIG. 13 is a longitudinal cross sectional view thereof;

FIG. 14 is an enlarged top detail taken from FIG. 13 ;

FIG. 15 is an enlarged bottom detail taken from FIG. 13 ;

FIG. 16 is an exploded top perspective view of the upper portion of thecask and impact limiter;

FIG. 17 is an exploded bottom perspective view of the lower portion ofthe cask and impact limiter;

FIG. 18 is an exploded bottom perspective view of the upper portion ofthe cask and impact limiter;

FIG. 19 is an exploded bottom perspective view of the lower portion ofthe cask and impact limiter;

FIG. 20 is an exploded top cross-sectional perspective view of the upperportion of the cask and impact limiter;

FIG. 21 is an exploded top cross-sectional perspective view of the lowerportion of the cask and impact limiter;

FIG. 22 is a top plan view of the perforation sleeve of the impactlimiter;

FIG. 23 is an enlarged detail taken from FIG. 22 ;

FIG. 24 is transverse cross sectional view taken from FIG. 23 ;

FIG. 25 is a computer generated image of the perforated sleeve after adrop test showing the deformed shape of the sleeve in the impact/crushzone;

FIG. 26 is a computer generated graph from the drop test showing theimpact deceleration time history of the cask;

FIG. 27 is a computer generated graph from the drop test showing thecask to ground (impact surface) time history;

FIG. 28 shows the cask with installed impact limiter loaded on atransport rail car;

FIG. 29 shows the core structure of a prior impact limiter design; and

FIG. 30 is a side cross-sectional of another embodiment of a perforatedsleeve of the impact limiter having a composite construction formed bywelding multiple ring segments of sleeves together at their inner andouter peripheries.

FIG. 31 is a front cross-sectional perspective view of an impactamelioration system for nuclear fuel storage according to the presentdisclosure including a transfer cask and fuel canister;

FIG. 32 is a side cross sectional view thereof;

FIG. 33 is an exploded view thereof;

FIG. 34A is a front elevation view thereof;

FIG. 34B is a detail taken from FIG. 34A;

FIG. 35 is a partial bottom view of the cask;

FIG. 36 is a partial top view of the cask;

FIG. 37 is a top perspective view of the bottom closure plate of thecask;

FIG. 38 is a side cross-sectional view of the bottom closure plate;

FIG. 39A is a side cross-sectional view showing an impact limiterassembly of the system comprising an impact limiter plug and mating plughole shown in FIGS. 31-34B;

FIG. 39B is a side cross-sectional thereof showing the plug in aninstalled pre-impact position;

FIG. 39C is a side cross-sectional thereof showing the plug in a deeperpost-impact position in the plug hole after application of an impactforce resulting from a cask drop event;

FIG. 40 is a cross-sectional perspective view of the cask bottom closureplate showing a second embodiment of a impact limiter assembly;

FIG. 41 is a detail taken from FIG. 40 ;

FIG. 42 is a cross-sectional perspective view of the cask bottom closureplate showing a third embodiment of the impact limiter assembly;

FIG. 43 is a detail taken from FIG. 42 ;

FIG. 44 is a perspective view of an exemplary nuclear fuel assembly ofthe type which may be stored in the canister.

FIG. 45 is perspective view of a pressure vessel in the form of anunventilated cask for nuclear waste fuel storage according to thepresent disclosure;

FIG. 46A is a partial cross sectional view thereof;

FIG. 46B is an enlarge detail taken from FIG. 46A;

FIG. 47 is a top view of the cask;

FIG. 48 is a longitudinal cross sectional view of the cask taken fromFIG. 47 ;

FIG. 49A is an enlarged detail showing the closure lid to cask interfaceand mounting details for securing the lid to the cask in a free floatingmanner, the lid being shown in a downward sealed position;

FIG. 49B is a similar view to FIG. 49A, but showing the lid in a raisedpressure relief position ajar from the cask;

FIG. 49C is a similar view to FIG. 49A, but showing one of the lid boltassemblies in exploded view;

FIG. 50 is a longitudinal cross sectional view of the cask taken fromFIG. 47 ;

FIG. 51 is a partial cross-sectional view of the cask closure lid;

FIG. 52 is an enlarged detail taken from FIG. 51 ;

FIG. 53 is a transverse cross sectional view of the lid;

FIG. 54 is an exploded perspective view of the cask;

FIG. 55 is a side elevation view of the cask;

FIG. 56 is a side elevation view thereof showing parts of the caskclosure lid in exploded view;

FIG. 57 is a partial longitudinal cross sectional view of the caskshowing the nuclear waste fuel canister positioned in the internalcavity of the cask;

FIG. 58 is a perspective view of one of the lifting rib plates of thecask configured for use with the lid bolt assembly;

FIG. 15 59 is a bottom exploded perspective view of the lid and upperportion of the cask; and

FIG. 60 is a top exploded perspective view of the lid and upper portionof the cask.

FIG. 61 is top perspective view of a polygonal cask configured forstorage of nuclear waste materials according to one embodiment of thepresent disclosure;

FIG. 62 is an enlarged detail taken from FIG. 61 ;

FIG. 63 is a bottom perspective view of the cask of FIG. 61 ;

FIG. 64 is an exploded top perspective view thereof showing the lidremoved;

FIG. 65 is an exploded bottom perspective view thereof;

FIG. 66 is a longitudinal side elevation view thereof;

FIG. 67 is a lateral end elevation view thereof;

FIG. 68 is a top plan view thereof;

FIG. 69 is a bottom plan view thereof;

FIG. 70 is a longitudinal transverse cross-sectional view thereof;

FIG. 71 is an enlarged detail taken from FIG. 70 ;

FIG. 72 is a top perspective view of the closure lid;

FIG. 73 is an enlarged top perspective view of an end portion of thelid;

FIG. 74 is a bottom perspective view of the lid;

FIG. 75A is a top exploded perspective view of the lid;

FIG. 75B is an enlarged detail taken from FIG. 75A;

FIG. 76 is a bottom exploded perspective view of the lid;

FIG. 77A is a partial longitudinal cross sectional view of the lidshowing the cask locking mechanism in a locked position or state;

FIG. 77B is a partial longitudinal cross sectional view of the lidshowing the cask locking mechanism in an unlocked position or state;

FIG. 78 is an enlarged detail in perspective view of a portion of thecask interior at the top opening showing the cask body lockingprotrusion arrangement;

FIG. 79 is an exploded perspective view of a portion of a longitudinalsidewall of the cask body showing a locking handle assembly in explodedview as well;

FIG. 80 is an enlarged perspective view of the locking handle assemblyin the inward blocking position locked with a cable-lock securitytag/seal in place;

FIG. 81 is a second enlarged perspective view of the locking handleassembly in the outward non-blocking position on the cask body;

FIG. 82 is an enlarged detail in perspective view of a portion of thecask interior at the top opening in a corner region showing the caskbody locking protrusion arrangement on adjoining walls of cask body;

FIG. 83 is a transverse cross sectional view of the cask body and lidshowing the lid removed;

FIG. 84 is an enlarged detail taken from FIG. 83 showing the lockinghandle assemblies on the longitudinal sidewalls of the cask body in theoutward non-blocking position;

FIG. 85 is a transverse cross sectional view of the cask body and lidshowing the lid in position on the cask body;

FIG. 86 is an enlarged detail taken from FIG. 85 showing the lockinghandle assemblies in the inward blocking position;

FIG. 87 is a perspective view of an actuator assembly for moving lockingbars of the lid;

FIG. 88 is a cross sectional view thereof;

FIG. 89 is a first schematic diagram of a sequential method for lockingthe cask of FIG. 61 ;

FIG. 90 is a second schematic diagram thereof;

FIG. 91 is a third schematic diagram thereof; and

FIG. 92 is a fourth schematic diagram thereof.

All drawings are schematic and not necessarily to scale. Features shownnumbered in certain figures which may appear un-numbered in otherfigures are the same features unless noted otherwise herein.

DETAILED DESCRIPTION

The features and benefits of the invention are illustrated and describedherein by reference to non-limiting exemplary (“example”) embodiments.This description of exemplary embodiments is intended to be read inconnection with the accompanying drawings, which are to be consideredpart of the entire written description. Accordingly, the disclosureexpressly should not be limited to such exemplary embodimentsillustrating some possible non-limiting combination of features that mayexist alone or in other combinations of features.

In the description of embodiments disclosed herein, any reference todirection or orientation is merely intended for convenience ofdescription and is not intended in any way to limit the scope of thepresent invention. Relative terms such as “lower,” “upper,”“horizontal,” “vertical,”, “above,” “below,” “up,” “down,” “top” and“bottom” as well as derivatives thereof (e.g., “horizontally,”“downwardly,” “upwardly,” etc.) should be construed to refer to theorientation as then described or as shown in the drawing underdiscussion. These relative terms are for convenience of description onlyand do not require that the apparatus be constructed or operated in aparticular orientation. Terms such as “attached,” “affixed,”“connected,” “coupled,” “interconnected,” and similar refer to arelationship wherein structures are secured or attached to one anothereither directly or indirectly through intervening structures, as well asboth movable or rigid attachments or relationships, unless expresslydescribed otherwise.

As used throughout, any ranges disclosed herein are used as shorthandfor describing each and every value that is within the range. Any valuewithin the range can be selected as the terminus of the range. Inaddition, any references cited herein are hereby incorporated byreference in their entireties. In the event of a conflict in adefinition in the present disclosure and that of a cited reference, thepresent disclosure controls.

As used herein, the terms “seal weld” or “seal welding” shall beconstrued according to its conventional meaning in the art to be acontinuous weld or process which forms a gas-tight joint between theparts joined by the weld and may be used to form hermetically sealedcavities or chambers.

Multiple Inventive Concept Roadmap

Multiple broad inventive concepts are disclosed herein and aredistinguished from one another using different sections each having anappropriately descriptive section header in the description anddiscussion that follows. Specifically, FIGS. 1-30 are relevant to abroad First Inventive Concept, FIGS. 31-44 are relevant to a broadSecond Inventive Concept, FIGS. 45-60 are relevant to a broad ThirdInventive Concept, and FIGS. 61-92 are relevant to a Fourth InventiveConcept. The broad inventive concepts should each be considered inisolation from one another. Each broad inventive concept may comprisemultiple inventive sub-concepts and embodiments within which may bedesignated by descriptive sub-headers in some instances. It is possiblethat there may be conflicting language or terms used between thedescriptions of each of the inventive concepts. For example, it ispossible that in the description of the First Inventive Concept aparticular term may be used to have one meaning or definition and thatin the description of the Second Inventive Concept the same term mightbe used to have a different meaning or definition. In the event of suchconflicting language, reference should be made to the particulardisclosure of the relevant inventive concept being discussed under eachsection heading which should be used and is controlling for interpretingthe language and terms used in the description of that particularrelevant inventive concept. Similarly, the section of the descriptiondescribing a particular relevant inventive concept being claimed shouldbe used and is controlling to interpret the respective claim languagewhen necessary.

First Inventive Concept

Nuclear Waste Cask with Impact Protection

Reference is made generally to FIGS. 1-30 which are relevant to FirstInventive Concept described below.

Because the extent of crush depth available in the radial direction ofthe cask is limited by the diameter of the impact limiter (which isconstrained by the size of the tunnels and bridges that the package mustpass through as previously described herein), the challenge to limit thedeceleration of the cask under horizontal or near-horizontal drop ismore acute. Limiting the peak g-load under the horizontal (side drop) ornear-horizontal (slap-down) angled drop conditions is the governingcondition in the impact limiter's performance. This is attributed to thefact that the fuel basket panels of the spent nuclear fuel canisterinside the outer cask have relatively limited capacity to withstand theinertia load of the fuel assemblies in their weak (lateral) direction.In the longitudinal direction, there is no such dimensional constraint;hence vertical and oblique (center of gravity or CG over the corner)drop orientations do not pose a similar challenge.

To overcome the challenge of limiting deceleration of the package from ahorizontal or near-horizontal fall, a new perforated impact limiterdesign and configuration which may comprise a perforation aluminum ringor sleeve in one non-limiting embodiment is disclosed. The term“aluminum” is used in a generic sense in this document meaning purealuminum or any of the many aluminum alloys available in the industry.

As further described below, the present perforated aluminum impactlimiter is an assemblage comprising an essentially annular shapedcylindrical body of certain height and diameter that slides over the topand bottom ends of the cask's machined end flanges or forgings asfurther described herein. The impact limiter generally comprises anouter cap shell and an internal perforated core comprising in oneembodiment an annular cylindrical perforated barrel or sleeve. Theperforated sleeve may have a monolithic body comprising a centralopening configured to slip over the top and bottom ends of the caskbody. The “donut-shaped” perforated sleeve includes a plurality ofelongated perforations forming longitudinal passages through the solidbody of the sleeve. The passages have a greater longitudinal length thantheir respective diameters, as further described herein. The passagescircumferentially extend 360 degrees around the entire sleeve in oneembodiment. The longitudinal passages may be arrayed in a staggeredpitch and may be tightly packed in one embodiment such that pitchspacing between adjacent perforations is not greater than the diameterof the smallest adjacent perforation. Accordingly, in one preferredpattern and pitch or hole spacing between perforations, a radialreference line drawn from the geometric center of the perforated sleeveoutwards through the sleeve will intersect at least one perforationregardless of angular orientation of the reference line. In other words,the reference line cannot be drawn through any angular position from 0to 360 degrees which will not pass through at least one perforation. Thesolidity ratio, “S” (defined as the ratio of the solid metal area formedby webs of material between the perforations to the total transversecross-sectional area of the sleeve), provides the parameter that can bevaried to achieve the required crush force resistance/crush performance.

In contrast to the cross-core honeycomb panel constructions of the pastas previously described herein, solid aluminum as a non-limiting metalof choice in one preferred embodiment is universallycommercially-available in a host of product forms and is obtainable innumerous common alloy compositions with well-characterized and knownprecise mechanical properties. Advantageously, this makes the crush orimpact resistance of the impact limiter more readily amendable toengineering analysis and computer modeling, and more predictable inimpact performance than composite structures such as the past honeycombdesign. In contrast to wood-based impact limiters, the present aluminumimpact limiter is essentially temperature-insensitive in the rangeapplicable to cask transport conditions (−40 C to 100 C) and subject toonly minimal change in their strength moduli under dynamic (impact)conditions.

The present perforated aluminum impact limiter has several criticallyimportant advantages over its honeycomb predecessor. Because aluminum isan isotropic material (i.e. identical values of mechanical properties inall directions), the impact limiter is assured to have essentially aradially symmetric crush property. In contrast, the honeycomb is anorthotropic material which imparts a certain variation in the crushcharacteristic of the impact limiter in the circumferential direction.Advantageously, an impact limiter with a radially symmetric crushstrength provided by the present perforated aluminum sleeve design willdeform uniformly regardless of the location of the impact force on theimpact limiter unlike the honeycomb design. Unlike the honeycombproduct, the present perforated aluminum impact limiter does not requireany adhesives which therefore does not suffer in impact performanceeffectiveness in the event of a fire during transport or otherwisecompared to its honeycomb counterpart.

FIGS. 1-24 depict various aspects of a nuclear waste transport cask 20with impact protection according to the present disclosure. Cask 20 maybe used for storing any type of radioactive high level nuclear waste,including spent nuclear fuel (SNF) or other forms of radioactive waste.The cask is constructed to provide radiation shielding to ameliorate thegamma and neutron radiation emitted by the decaying spent nuclear fuel(SNF) or other high level radioactive waste held in the inner fuelstorage canister 30 contained inside the cask. Cask 20 may be anycommercially-available storage and/or transport cask, such as forexample without limitation HI-STAR or HI-STORM casks available fromHoltec International of Camden, N.J. or other. The SNF canister 30 maybe any commercially-available waste canister such as a multi-purposecanister (MPC) also available from Holtec International or other.

Cask 20 has a vertically elongated and metallic cylindrical bodyincluding an open top end 21, a bottom end 23, a cylindrical sidewall 24extending between the ends, and an internal cavity 28. The cylindricalmetallic SNF canister 30 (represented schematically by dashed lines andwell known in the art) containing radioactive SNF fuel assemblies orother nuclear waste W is insertable into cavity 28 through top end 21,which is then closed by a bolt-on top lid assembly 25 to seal the cask20. Cavity 28 extends for a full height of the cask in one embodiment.The cavity 28 is configured (e.g. transverse cross-sectional area) tohold only a single SNF canister 30 in one embodiment.

The upper and lower extremities of cask 20 further include top andbottom end forgings 37, 38. Top end forgoing 37 has an annular structuredefining a central opening for inserting the SNF canister 30therethrough into cavity 28 of the cask. Bottom end forgoing 38 has asolid disk-like structure defining a centrally-located and circularbottom baseplate 29. Baseplate 29 disposed at the bottom end of the caskbody forms a floor and support surface inside cavity 28 on which the SNFcanister is seated. The cask body 21 including the forgings 37, 38, andinner shell 24 a (described below) may be formed of steel, such asstainless steel which is effective at blocking gamma radiation.

In one embodiment, baseplate 29 (bottom end forging 38) defines adownwardly open recess 29 a which receives a circular disk-shapedradiation shielding plate 31 formed of radiation shielding material. Theshielding material may be a boron-containing material such as Metamic®or Holtite™ (each a proprietary product of Holtec International ofCamden, N.J.); the latter of which generally comprises hydrogen richpolymer impregnated with boron carbide particles for neutron shielding.Metamic® is a discontinuously reinforced aluminum boron carbide metalmatrix composite material designed for neutron radiation shielding.Either shielding material is effective for neutronscattering/attenuation. Other neutron scattering/attenuation materialmay be used. In one embodiment, the radiation shielding plate 31 may beHoltite™.

Top lid assembly 25 may include a inner lid 26 and outer lid 27 in oneembodiment. Both the inner and outer lids are recessed into the top endof the cask body 21, more particularly top end forging 37, such that thelids do not protrude above the top end 21 of the cask. Lids 26 and 27may be stacked on top of each other in abutting contact in onearrangement. Inner lid 26 may have a smaller outer diameter than theouter lid 25 which allows each lid to be fastened to a differentcircumferentially-extending annular surface of the top end forging 37.Inner lid 26 may be bolted onto the top end forging 37 by a firstcircumferential array of threaded fasteners 28 such as bolts. Outer lid27 may be bolted onto the top end forging of the cask by a secondcircumferential array of threaded fasteners 28 such as bolts which fallon a different bolt circle outside the bolt circle formed by the boltsfor the inner lid. Inner and outer lids 26, 27 may be formed of metalsuch as steel (e.g. stainless steel in one embodiment) and has asubstantial thickness selected to effectively block gamma radiationemitted by the canister 30. The inner and outer lids 26, 27 may beformed of steel such as stainless steel in some embodiments.

The sidewall 24 of cask 20 may be formed by multiple verticallyelongated cylindrical shells and radiation shielding materials.Alternatively, sidewalls 24 may be collectively formed by a plurality ofaxially aligned and vertically stacked cylindrical shell segments sealwelded together at the joints therebetween to form an elongated shellassemblage. In one embodiment, the cask body may be a compositeconstruction generally comprising a structural inner shell 24 a,intermediate gamma shield 24 b, and outer neutron shielding jacket 40.Shell 24 a, gamma shield 24 b, and jacket 40 may be generally annularand cylindrical in shape, and are concentrically aligned with each otherand longitudinal axis LA of cask 20.

Inner shell 24 a may be formed of a structural metal such as steel (e.g.stainless steel or other) which forms the innermost part of sidewall 24whose interior surface forms the cavity 28 of the cask which holdsnuclear waste canister 30. The intermediate gamma shield 24 b may beformed of a radiation shielding material, and more particularly a gammashielding material effective for blocking gamma radiation emitted by theSNF stored in nuclear waste container 30 held inside the cask 20.Intermediate shield 24 b may be formed of lead of suitable thickness insome embodiments. However, other dense gamma blocking materials such asconcrete, copper, suitably thick steel, etc. may alternatively be usedas some non-limiting additional examples. The inner shell 24 a and gammashield 24 b may be in substantial conformal contact in some embodimentsas shown, or alternatively may be radially spaced apart forming anannular gap therebetween. Both the inner shell and gamma shield formedof dense steel and lead material types described above are eacheffective for gamma blocking applications. The inner steel shell 24 aprovides the bulk of the structural support of the cask sidewall 24 andis welded to top and bottom end forgings 37, 38.

The cylindrical outer neutron shielding jacket 40 extends perimetricallyand circumferentially around the sidewall 24 of cask 20 between the topand bottom ends of the cask. The jacket may extend longitudinally forsubstantially the entire height of the cask. The jacket 40 may be formedof a boron-containing neutron shielding material such as Metamic® orHoltite™ (each a proprietary product of Holtec International of Camden,N.J.). These materials were previously described herein and areeffective for neutron scattering/attenuation. In one embodiment, thejacket may be formed of Holtite™. Other neutron scattering/attenuationmaterial may be used. In some constructions, the jacket 40 may be formedby two or more arcuate segments which are coupled together such as viawelding or mechanical fastening methods. An outer metallic shellenclosure 41 which encases the neutron shielding jacket 40 may beprovided in some embodiments for protection of the neutron shieldingmaterial.

Outward facing upper and lower impact load bearing surfaces 35, 36 areformed by exposed side portions of top and bottom end forgings 37, 38 ofcask 20 above and below the neutron shielding jacket 40 in oneembodiment as shown. The end forgings may be seal welded to the top andbottom ends of the inner shell 24 a. Bearing surfaces 35, 36 extendcircumferentially around the entire perimeter of the cask and faceradially/laterally outwards. In one embodiment, the bearing surfaces maybe formed by annular stepped portions 22 of the cask sidewall 24 at thetop and bottom ends 21, 23 of the cask 20. The bearing surfaces 35, 36represent reduced diameter stepped end portions of the cask 20 formed bythe end forgings 37, 38 having a smaller outside diameter than theoutside diameter of shielding jacket 40 on the main middle portion ofthe cask sidewall. Bearing surfaces 35, 36 are therefore recessedradially inwards from the adjoining full diameter portions of the casksidewall 24 below the upper bearing surface 35 and above the lowerbearing surface 36 as shown.

Pairs of upper and lower lifting lugs or trunnions 32 may be providedfor lifting, transporting, and loading the cask 20 onto the rail car orother movable carrier via a motorized cask crawler typically driven bytank-like tracks for hauling the extremely heavy casks (e.g. 30 ton ormore). Such robust cask crawlers are well known in the art without needfor further elaboration and conventionally used for transporting andraising/lowering casks at a nuclear reactor facility (e.g. powergeneration plant or other) or interim nuclear waste storage facility.Cask crawler transporters are commercially-available from manufacturerssuch as J&R Engineering Co. of Mukwonago, Wis. (e.g. LIFT-N-LOCK®) andothers. The trunnions 32 are rigidly attached to the inner steel shell24 a of the cask 20 such as via welding or another rigid couplingmethod.

The top and bottom impact limiters 50 according to the presentdisclosure will now be described. FIGS. 13-24 show the impact limitersand aspects thereof in greater detail.

Each impact limiter 50 generally comprises an outer protective cap shell51, impact-absorbing core comprising perforated sleeve 80, and annularclosure plate 70. Cap shell 51 in one embodiment includes a circular endwall 52 and a cylindrical sidewall 53 extending longitudinally from theend wall parallel to longitudinal axis LA of cask 20. End wall 52defines an outer surface 58 including a plurality of fastener openings57 to access fasteners used to secure the impact limiters 50 to cask 20,as further described herein. An innermost end of sidewall 53 oppositethe end wall 52 (i.e. end of the sidewall proximate to cask 20 whenimpact limiter is mounted) defines an annular edge 59.

Cap shell 51 defines an internal end cavity 51 a which is filled with asuitable energy absorbing material 45 that is crushable to dissipateexternal impact forces which might be caused by an end drop of the cask20 (i.e. vertical drop on cask on end or slight oblique angle thereto).The energy absorbing material 45 may be a suitable preferablyfire-resistant energy absorbing substance or structural assemblage. Inone embodiment, the energy absorbing material may be a conventionalhoneycomb impact limiter formed by cross-laid corrugated aluminum panels10 as previously described herein and shown in FIG. 29 . In thisapplication, the honeycomb arrangement of panels is used for cask endimpact situations while side drop impact protection is provided by theperforated sleeves 80 further described herein collectively forming ahybrid impact limiter. The panels 10 would be oriented such that theplane of each panel is oriented perpendicularly to longitudinal axis LAof the cask (i.e. cross-wise). Open areas between the panels wouldtherefore be arranged in the lateral/radial direction, notlongitudinally. In another embodiment, the energy absorbing material 45may be a crushable polymeric foam material of suitable density (e.g.polyethylene, etc.). In one embodiment, the energy absorbing material 45may fill the end cavity 51 a such that the material has a longitudinalthickness substantially greater than perforated sleeve 80, and maycomprise a majority of the total longitudinal height of the cap shell51. In some cases, the shell 51 may further provide structural supportto the impact limiter assembly. In one construction, an annular spacer71 may be provided which forms an annular gap between the end wall 52 ofthe cap shell 51 and the perforated sleeve 80 to space the sleevelongitudinally apart from the end wall (see, e.g. FIGS. 14-15 ).

Cap shell 51 may be formed of a suitable metal, such for example withoutlimitation thin gauge stainless steel. Other metal materials includingsuitable gauge aluminum or other can be used. The cap shell provides aprotective outer skin that encloses the energy-absorbing perforatedsleeve 80 and energy absorbing material 45 at the outboard ends of theimpact limiters 50 which shields the sleeve and energy absorbingmaterial from minor damage, fire, and weather during transport andhandling.

Cap shell 51 includes a centrally-located cylindrical collar 55 definingan open circular receptacle 56. Collar 55 projects inwardly in alongitudinal direction from the end wall 52 of the cap shell towards thecask 20. Collar 55 is spaced radially inward from sidewall 53 to definean open annulus 54 configured for receiving and mounting perforatedsleeve 80 therein. Sleeve 80 becomes fully nested within the annulus 54and cap shell 51 when positioned in the impact limiter 50. Perforatedsleeve 80 is located inboard of end wall 52 for both the top and bottomimpact limiters. Once the perforated sleeve is mounted in annulus 54,closure plate 70 may be welded to annular edge 59 and/or collar 55 toretain the sleeve in the cap shell.

The impact limiters 50 may be detachably mounted to the lid assembly ofthe cask 20 via a plurality of threaded fasteners 60 such as bolts.Fasteners 60 may be supported by a circular metallic bolting plate 64positioned inside circular receptacle 56 formed in the cap shell 51 bycollar 55. Fasteners 60 project towards the cask 20 from bolting plate64 in receptacle 56 to threadably engage corresponding threaded socketsor bores 61 formed in the upper outer lid 27 and the baseplate portionof the bottom end forging 38 when the top and bottom end forgings ofcask 20 are insertable received in central receptacle 56 of the impactlimiters. The enlarged heads of the bolts do not pass through boltingplate which may be welded to the collar 55 while the threaded shanks ofthe bolts pass through respective openings in the bolting plate toproject inwards from the bolting plate to threadably engage the cask(see, e.g. FIGS. 14 and 15 ). Bolting plate 64 may be formed of asuitably strong metal, such as without limitation carbon or stainlesssteel for strength. The bolting plate 64 is compressed by the impactlimiter fasteners 60 against the uppermost exposed outer lid 27 of cask20 at top and radiation shielding plate 31 at the bottom of the caskwhen the impact limiter 50 is detachably coupled thereto.

Bolting plate 64 may be spaced longitudinally apart from energyabsorbing material 45 in one embodiment. A circular radiation shieldingdisk 63 with bolt holes may be interposed between bolting plate 64 andthe energy absorbing material. Radiation shielding disk may be formed ofa radiation shielding material effective for neutron attenuation, suchas without limitation Holtite™ previously described herein. Otherneutron absorbing materials or gamma blocking materials such as lead maybe used in other embodiments depending on the radiation shielding needs.In other embodiments, the shielding disk 63 may be replaced by a disk ofthermal fire-resistance insulation for added protection of the caskagainst a fire event. Longitudinally-extending fastener openings 57formed through the energy absorbing material 45 of each impact limiterprovide access to the fasteners 60 for tightening and coupling theimpact limiters 50 to the cask 20. The bottom radiation shielding plate31 of cask 20 may also include a plurality of longitudinally-extendingfastener openings 62 which permit the fasteners to reach and access thethreaded bores 61 in the bottom end forging 38 (see, e.g. FIG. 15 ).

When mounted on cask 20, the impact limiters 50 have an outside diameterD1 which is larger than the outside diameter D2 of the cask (defined bythe exterior surface of radiation shielding jacket 40 (identified inFIG. 13 ). The outside diameter D3 of the perforated sleeve 80 similarlyis larger than cask outside diameter D2. Accordingly, the impactlimiters are configured to each protrude radially outward beyond thebody of cask to protect the cask if dropped. The deformable impactlimiters, and not the cask, will first strike the impact surface (e.g.ground or concrete slab generally) to absorb and dissipate he impactforce or kinetic energy of the fall.

Perforated sleeve 80 may have an annular body 80 a formed of a basemetal such as without limitation aluminum or aluminum alloy in onenon-limiting preferred embodiment. The body may, be a solid metalmonolithic body of unitary structure in one embodiment. Thisconstruction advantageously allows the perforated sleeve to absorb andmechanically deform in response to an external impact force as anintegral solid unit in a directionally uniform manner.

In other possible constructions, the body of perforated sleeve 80 may beformed by composite construction formed by multiple stacked and weldedannular metal ring segments having the same mounting and impactabsorbing features as the monolithic sleeve described further below.FIG. 30 shows one non-limiting example of such a compositionconstruction. The segmented perforated sleeve comprises at least tworing segments 80-1, 80-2 which are abuttingly engaged and stacked uponeach other at a flat-to-flat interface between mating major end surfaces87 of the ring segments which form a joint 95 therebetween. The segments80-1, 80-2 may be welded together at their inner and outercircumferential peripheries. More specifically, welds may be formedbetween the annular abutting outer circumferential walls 85 of theabutted segments at the exposed outboard portions 95 a of the joint 95.Welds may also be formed between the annular abutting innercircumferential wall 87 within central opening 82 of the segments 80-1,80-2 at the exposed inboard portions 95 b of the joint. Intermittentstitch welds spaced circumferentially apart or full circumferentialwelds may be used to permanently join the ring segment; both weldingmethods of which are well known in the art without further explanation.The composite perforated sleeve 80 may be built in segments to thedesired height of the sleeve by permanently joining a suitable number ofsegments together of individual height. The array of collapsibleperforations in each ring segment would be concentrically aligned witheach other in the stack to form continuous longitudinal passages 81which extend for the full height of the stack and perforated sleeve 80.

With continuing general reference now to FIGS. 1-24 , the perforatedsleeve body 80 a may comprise a central opening 82 and a circumferentialarray of perforations comprising elongated longitudinal passages 81formed between flat and parallel opposing major end surfaces 84 of thebody. Central opening 82 receives the top and bottom ends 21, 23 of cask20. Passages 81 may extend completely through the major end surfaces inone non-limiting preferred embodiment; however, in other possibleembodiments the passages 81 may extend only partially through annularbody of the sleeve. Cylindrical outer circumferential wall 85 and innercircumferential wall 87 extend longitudinally between the major endsurfaces 84 of the perforated sleeve 80 parallel to longitudinal axisLA. The inner circumferential wall 87 of perforated sleeve 80 defines aninward facing annular load transfer surface 86 which engages the annularouter surface 55 a of collar 55 facing outward towards annulus 54 whenthe sleeve is positioned in the annulus of impact limiter 50. Theopposite annular inner surface 55 b of collar 55 facing inward towardreceptacle 56 is positioned to engage the top and bottom outward facingannular impact load bearing surfaces 35, 36 of cask 20 when the impactlimiters 50 are installed on the cask.

The impact sleeve 80, collar 55, and bearing surfaces 35, 36 of the caskare laterally/radially aligned when the impact limiters 50 are mountedon the top and bottom ends of the cask (see, e.g. FIGS. 10-11 ). Thisallows the radially inward directed impact load or force resulting froman impact event to be distributed radially through the impact sleeve 80to the cask to be absorbed by, the more structurally robust top andbottom end forgings 37, 38 rather than the steel inner shell 24 a, leadintermediate gamma shield 24 b, and outer boron-containing neutronshielding jacket 40. These latter components are structurally weaker inthe radial/lateral direction and/or thinner in lateral thickness thanthe end forgings 37, 38 as shown, and hence are more susceptible todamage due to impact loads which could breach the nuclear wastecontainment package (i.e. cask). Radially acting external impact forcesare transmitted through in turn (from outside to inside) the impactsleeve 80, to collar 55, and finally to the cask load bearing surfaces35, 36 of the cask end forgings 37, 38.

With continuing reference to FIGS. 13-24 , the longitudinal passages 81may be oriented parallel to each other and extend between major endsurfaces of the perforated sleeve 80. Accordingly, none of the passagesmay intersect any other passages. In one embodiment, the longitudinalpassages may further be oriented parallel to the longitudinal axis LA ofthe cask when mounted thereon. In such an orientation, passages 81 areoriented perpendicular to the opposing major end surfaces 84 of theperforated sleeve 80. Longitudinal passages 81 may have a circulartransverse cross section which allows them to be readily formed bydrilling the solid metallic body of the perforated sleeve. However,other cross-sectional shapes are possible. The passages may each have alongitudinal length Lp which is greater than their respective diameterDp (see, e.g. FIGS. 23-24 ). In some non-limiting preferred embodiments,the longitudinal passages each have a length Lp greater than at leasttwo times their respective diameter Dp. This allows formation of alongitudinally thick perforated sleeve 80 for greater lateral andoblique impact resistance, and protection of the cask 20 in survivingfalls. The end wall 52 of impact limiter 50 may have a longitudinalthickness which is at least twice the longitudinal thickness ofperforated sleeve 50 in some embodiments.

The array of longitudinal passages 81 of perforated sleeve 80 may bedispersed in a full 360 degree pattern around an entirety of theperforated sleeve as best shown in FIG. 23 . In one embodiment, thearray of longitudinal passages 81 may be arranged in multiplecircumferentially-extending concentric rings Rn of longitudinal passageswhich extend circumferentially around the perforated sleeve. In someembodiments, at least 3 rings Rn may be provided. In the non-limitingillustrated embodiment, 7 rings are shown. Any suitable number of ringsmay be provided depending on the radial width of the perforated sleeve80, diameter Dp of the longitudinal passages 81, and other designfactors. Longitudinal passages 81 in each ring Rn may be uniformlyspaced apart in one implementation.

The longitudinal passages 81 may be arrayed in a triangular staggeredpitch or hole pattern as best shown in FIG. 23 . In certain embodiments,a 60 degree hole pattern may be used in which passages 81 in adjacentrings Rn are located at an acute angle A1 of 60 degrees to each other.Other angles and hole patterns may be used. The staggered hole patternallows a maximum number of passages 81 to be formed in perforated sleeve80 due to the circumferentially offset positioning of passages betweenadjacent rings Rn (i.e. a passage 81 in the next inward or outwardadjacent ring Rn to a present first ring under consideration is locatedbetween each of two passages in a first ring as shown). The result is atightly packed pattern of longitudinal passages 81 in the perforatedsleeve 80, thereby concomitantly maximizing the open area which can beprovided to control and maximize the deformability of the sleeve toabsorb lateral drop-induced impact loads/forces.

The longitudinal passages 81 in each concentric ring Rn may haveprogressively larger diameters than the inwardly immediate adjacent ringof longitudinal passages such that the diameters increase in size movingradially outwards from the geometric center C of perforated sleeve 80through the rings. Accordingly, in such a constructions, longitudinalpassages 81 of an outermost ring Rn each have larger diameters thanthose in an innermost ring of longitudinal passages closest to thegeometric center C and central opening 82 of perforated sleeve 80.Longitudinal passages 81 in diagonal rows Dr of passages 81 in thesleeve may be spaced at a hole pitch P1 which progressively gets largerbetween each adjacent ring Rn of passages moving in a radially outwarddirection from the central opening 82. In additional, the pitch P2between longitudinal passages 81 in each concentric ring of passages mayalso become progressively larger moving in a radially outward direction.Accordingly, the pitch P2 between passages 81 in the outermost ring Rnis larger than pitch P2 between passages in the innermost ring.

Referring to FIGS. 22-24 , longitudinal passages are separated by arelatively thin ligament or web 90 of material of the solid metallicbody of the perforated sleeve 80. A web thickness Ti is defined betweenadjacent longitudinal passages 81 which is measured perpendicularly tothe passage lengths Lp as shown in FIG. 23 (perpendicularly tolongitudinal axis LA of cask). The webs 90 extend fully between theopposing major surfaces 84 of the perforated sleeve between the passages81. In various embodiments, the webs 90 between adjacent passages 81 maypreferably, be smaller in thickness Ti than the diameter Dp of thelargest diameter longitudinal passage, and more preferably smaller thanthe smaller diameter longitudinal passage (i.e. innermost ring Rn ofpassages). The thin webs 90 in conjunction with the hole pattern andpitch (spacing) between longitudinal passages 81 result in a tightlypacked perforations such that a radial reference line R drawn from thegeometric center of the perforated sleeve 80 outwards through anyportion of the sleeve will intersect at least one perforation regardlessof angular orientation of the reference line.

The solidity ratio “S” is defined as the ratio of the solid metal areaformed by the webs 91 of material between the longitudinal passages 81divided by the total transverse cross-sectional area of the perforatedsleeve 80 (calculated across major end surfaces 84 perpendicular tolongitudinal axis LA). In one non-limiting preferred embodiment, thesolidity ratio S may be less than 0.5 resulting in an open area of thesleeve 80 collectively formed by the longitudinal passages 81 beinggreater than 50% and solid areas concomitantly being less than 50%. Thegreater the open area, the generally greater the ability of theperforated sleeve to deform under lateral impact loads or forces actingperpendicularly (lateral/horizontal cask drop) or obliquely (angled caskdrop) to the longitudinal axis LA of cask 20. In other embodiments whereless deformability might be required, the open area of sleeve 80 may beless than 50% and solid area greater than 50% resulting in more solidarea (i.e. solidity ratio greater than 0.5). As previously noted herein,the solidity ratio provides the engineering parameter that can be variedto achieve the required crush force resistance/crush performance of theperforated sleeve.

It bears noting that other hole patterns (e.g. square, etc.), othernon-polygonal or polygonal hole shapes (e.g. oblong slots, ellipses,squares, rectangles, triangles, hexagons, etc.) and hole pitches may beused in other embodiments contemplates. Accordingly, the invention isnot limited to the hole shape, hole pattern, or pitches describedherein.

Computer Testing/Analysis of Perforated Sleeve

To evaluate the crush performance of the perforated aluminum perforatedsleeve 80 of impact limiter 50 disclosed herein in lateral dropscenarios, a 109 metric ton cask protected during a lateral (horizontal)drop event (per 10 CFR 71.73) by the perforated sleeve was computeranalyzed. This so-called free drop accident postulates a fall from 30feet onto an essentially rigid surface. The following impact limitergeometry was computer modeled: Inner diameter of cylinder=86.75 inches;Outer diameter=123.75 inches; and Longitudinal Thickness (longitudinalmajor end surface to major end surface=13.0 inches”). The raw workpiececomprising a 6061-T6 aluminum ring (illustrated in FIGS. 22-24 ) wasdrilled with 7 rows of circular longitudinally-extending holes to formthe longitudinal passages 81. The diameters of the passages range from2.125 inches (innermost passages) to 2.875 inches (outermost passages)with an increment of 0.125 inch between adjacent circumferentialconcentric rings Rn previously described herein. There are 100longitudinal passages 81 of same diameter in each row. The solidityratio “S” of the perforated aluminum ring or sleeve used for the impactlimiter was 0.455.

The 30-feet lateral (horizontal) drop event is simulated on the computercode LS-DYNA. FIG. 25 shows the deformed crushed shape of the impactlimiter after the impact event. FIGS. 26 and 27 respectively show theimpact deceleration-time history plot of the cask and the cask to ground(target surface) time history (a zero gap at the end of the impact isundesirable). FIG. 26 shows the peak deceleration to be limited to about65 g's which indicates excellent impact limiter performance for thisclass of problems.

FIG. 28 shows cask 20 with impact limiters 50 on each end loaded onto atypical low-body rail car 100 (“low boy”) for transport. Cask 20 istransported in the horizontal position as shown to the intendeddestination site.

Aspects and contemplated variations of the impact limiter 50 utilizingthe perforated ring or sleeve 80 are as follows. The perforated sleeve80 may be made of a perforated aluminum that can be used to efficientlyextract the kinetic energy from a falling transport package—cask, so asto limit the deceleration suffered by its contents including the nuclearwaste container 30 with spent fuel assemblies (SNF) contained therein.Typical aluminum materials that are suited for this application innconstructing the perforated sleeve 80 include without limitation purealuminum (Al 1100), alloy 5052, alloy 6061 and alloy 6063, among others.Collectively, these materials are referred to as “soft isotopic”metallic materials. The perforated sleeve 80 can be manufactured bymachining (e.g. drilling or other method) the soft-isotopic materialcastings or plates to form the longitudinal passages 81. Extrudingblocks of the soft-isotopic material to form the ring shaped basematerial or workpiece prior to machining the passages may also be used.While circular perforations (longitudinal passages 81) in transversecross section are desirable due to simplicity in their formation, theperforations in sleeve 80 can be other cross-sectional shaped includingwithout limitation square, hexagonal or another fabricable geometricshape. Finally, in lieu of a cylindrical sidewall 85 as shown herein(i.e. straight and parallel to longitudinal axis LA), the perforatedsleeve 80 can have other shaped sidewalls such as without limitation afrustoconically tapered or stair-cased (multi-stepped) sidewall in theradial direction to obtain the desired crush-force relationship.

Second Inventive Concept

Impact Amelioration System for Nuclear Fuel Storage

Reference is made generally to FIGS. 31-44 which are relevant to theSecond Inventive Concept described below.

FIGS. 31-44 depict various aspects of an impact amelioration or limitersystem associated with nuclear waste storage systems comprising vesselsused in the storage of spent nuclear fuel (SNF) or other irradiated highlevel radioactive waste materials removed from the nuclear reactorcontainment. The amelioration system generally comprises an outertransfer overpack or cask 2100 and a waste fuel (e.g. SNF) canister 2120configured for storage inside the cask. Features of each storage vesseland the impact amelioration system will now be further described.

Canister 2120 may be used for storing any type of high level radioactivenuclear waste, including without limitation spent nuclear fuel (SNF) orother forms of radioactive waste materials removed from the reactor. TheSNF or simply fuel canister for short may be any commercially-availablenuclear fuel/waste storage canister, such as a multi-purpose canister(MPC) available from Holtec International of Camden, N.J. or other.

Canister 2120 has a vertically elongated and metallic body comprised ofa cylindrical shell 2121 extending along a vertical centerline Vc whichpasses through the geometric center of the shell. Canister 2120 includesa bottom baseplate 2122 seal welded to a bottom end of the shell, and anopen top 2126 which may be closed by an attached lid 2125 (schematicallyshown in dashed lines in FIG. 33 to avoid obscuring other aspects of theimage). Lid 2125 may be seal welded to a top end 2126 of the canistershell 2121 to form a hermetically sealed cavity 2127 inside thecanister. The foregoing canister parts may be formed of any suitablemetal, such as for example without limitation steel including stainlesssteel for corrosion protection.

Fuel basket 2123 is disposed in cavity 2127 of the canister 2120 and isseated on the bottom baseplate 2122 as shown. The fuel basket may bewelded to the baseplate for stability in some embodiments. In someembodiments, the baseplate 2122 may extend laterally outwards beyond thesides of the fuel basket 2123 around the entire perimeter of the fuelbasket as shown.

The fuel basket 2123 is a honeycomb prismatic structure which in oneembodiment may be formed by a plurality of interlocked and orthogonallyarranged slotted plates 2123 a built up to a selected height invertically stacked tiers. The plates of fuel basket 2123 define a gridarray of plural vertically-extending openings forming fuel assemblystorage cells 2124. Each cell is configured in cross-sectional area andshape to hold a single U.S. style fuel assembly 28, which containsmultitude of spent nuclear fuel rods 28 a (or other nuclear waste). Anexemplary fuel assembly of this type having a conventional rectilinearcross-sectional configuration is shown in FIG. 44 . Such fuel assembliesand the foregoing fuel basket structure are well known in the industry.The open cells 2124 of the fuel basket are defined by the orthogonallyintersecting slotted plates 2210, and therefore have a concomitantlyrectilinear cross-sectional shape (e.g. square). This gives the fuelbasket an overall compound rectilinear polygonal shape in transversecross section as shown which includes multi-faceted and stepped exteriorperipheral side surfaces collectively defined by the flat lateralperipheral sidewalls of the outermost exterior slotted plates 2123 a.

Transfer cask 2100 has a vertically elongated metallic body including acylindrical shell 2101, circular top closure plate 2102 attached to thetop end of the shell, and a circular bottom closure plate 2103 attachedto the bottom end of the shell. A top ring plate 2107 may be providedwhich is fixedly attached to the top end of shell 2101 such as viawelding. A bottom ring plate 2106 may be fixedly attached (e.g. sealwelded) to the upper or top surface 2105 of the bottom closure plate2103 at its periphery; which ring plate in turn is fixedly attached(e.g. seal welded) to the bottom end of the shell 2101. The top closureplate 2102 may also be seal welded to the shell 2101, or in someembodiments may instead be bolted and gasketed to the cask instead toprovide easier access to the canister 2120. An internal cavity 2104 isdefined by the cask which extends for a full height of the cask. Thecavity 2104 is configured in dimension and transverse cross-sectionalarea to hold only a single fuel canister 2120 in some embodiments as isconventional practice in the art.

The circular bottom closure plate 2103 of cask 2100 may be consideredsomewhat cup-shaped in one embodiment in view of the raised bottom ringplate 2105 which rises up a short distance above the horizontal flat topsurface 2105 of the bottom closure plate. This construction defines arecessed canister seating area 2108 which helps center and stabilize thecanister 2120 when loaded into the cask. The bottom baseplate 2122 ofcanister 2120 is at least partially received in the recessed canisterseating area as shown in FIGS. 31 and 32 .

The cask 2100 is a heavy radiation shielded storage vessel. Thecylindrical shell 2101 of cask 2100 forms a sidewall which may have acomposite construction including an outer shell member 2109, inner shellmember 2110, and radiation shielding material(s) 2111 disposed betweenthe shell members. In some embodiments, the shielding material 2110 maycomprise concrete, lead, boron-containing materials, or a combination ofthese or other materials effective to block and/or attenuate gamma andneutron radiation emitted by the nuclear waste (e.g. fuel assemblies)stored in canister 2120 when loaded into the cask 2100. Any suitabletypes, thicknesses, and arrangement of shielding materials may be usedto provide the necessary degree of shielding.

The outer and inner shell members 2109, 2110 of the cylindrical shell2101 of cask 2100 may be formed of a suitable metal such as steel. Thetop and bottom closure plates 2102, 2103, and the top and bottom ringplates 2107, 2106 may similarly be formed of metal such as steel.

In conventional cask construction and deployment, the canister is seateddirectly onto the bottom closure plate of the cask 2100 in an abuttingrelationship. A flat to flat interface is formed between the entirety ofthe bottom baseplate of the canister and the bottom closure plate of thecask. In the event the cask with canister loaded therein is dropped ontoan immovable/stationary hard surface (e.g. top of concrete slab 2115 orother relatively hard/compacted material) as shown in FIG. 31 , there isno impact protection for the canister which might decrease the g-load orforce resulting from the impact force of the cask striking the surface.The kinetic energy of the resultant impact force generated by the dropis transmitted through the bottom closure plate of the cask directly tothe baseplate of the canister and then to fuel assemblies therein, whichtypically rest directly on the baseplate. The structural integrity ofthe nuclear fuel assemblies and SNF therein are therefore exposed todamage due to the unmitigated g-load or forces resulting from the dropevent.

The present disclosure provides an impact amelioration or limitingsystem configured to absorb and minimize the actual g-load/forcetransmitted through the cask 2100 during a drop event to protect thefuel canister 2120. With continuing general reference to 31-43, theamelioration system may comprise a plurality of impact limiterassemblies arranged at the lower canister to cask interface (i.e. bottomof canister baseplate 2122 to top of cask bottom closure plate 2103).

In one embodiment with specific initial reference to FIGS. 31-39C, theimpact limiter assemblies 2130 each comprise an impact limiter rod orplug 2130 and a corresponding plug hole 2140. Plug holes 2140 may becomplementary configured to the plugs 2131 in shape/profile. In oneembodiment, the sides of the plugs and plug holes may each be tapered.In one embodiment, the plugs 2131 may have a frustoconical shape and atleast a portion of the plug holes 2140 may have a complementaryfrustoconical shape. In the embodiment shown in FIGS. 39A-C, the entireplug hole 2140 is frustoconical in shape from top to bottom.

The impact limiter plugs 2131 may comprise a solid body including a topsurface 2132, bottom surface 2133, and sides 2134 extendingtherebetween. The top surface may be flat and larger in surface areathan the bottom surface defining an overall wedge-shaped plug. Thebottom surface 2133 may also be flat as shown and parallel to the topsurface 2132. Accordingly, sides 2133 may be tapered having an angle oftaper A1 which defines a plug body having a frustoconical shape asshown.

Plug holes 2140 may be complementary configured to the plugs 2131. Plugholes 2140 comprise an open top 2141 configured for at least partiallyreceiving and embedding the plugs 2131 therein, a flat closed bottom2142 formed by the cask bottom closure plate 2103, and tapered sidewalls2143 extending therebetween. The open top may have larger projected openarea than the closed bottom defined by bottom surface 2144 of the plughole defining a wedge-shaped hole. Accordingly, sidewalls 2143 of plughole 2140 may be tapered having an angle of taper A2 which defines aplug hole having a frustoconical shape as shown. In certain embodiments,angle of taper A2 of the plug holes 2140 may be the same as the angle oftaper A1 of the impact limiter plugs 2131. The plugs however may have amaximum diameter D1 defined by the top surface 2132 which is slightlylarger than the diameter D2 of the open top 2141 of plug holes 2140 suchthat the plugs cannot fully enter the plug holes and contact theirbottom surfaces 2144 (see, e.g. FIG. 39B in the pre-impact embedmentposition of the plugs in the holes). The slight oversizing of the plugs2131 and mating tapers of the plugs and their associated plug holes 2140create frictional engagement therebetween the mutually engaged plugsides 2134 and plug hole sidewalls which retains the plugs in positionspaced vertically above from the bottom surface 2144 of the plug holes.The bottom surface 2133 of plugs 2131 may also be larger in diameterthan the bottom surface 2142 of the plug holes 2140. Accordingly, theslightly larger diameter plugs 2131 are prevented from slippingcompletely into the plug holes 2140 to the bottom even though the angleof tapers A1, A2 may be the same for each feature (see, e.g. FIG. 39Bpre-impact frictionally engaged position of plugs).

In certain exemplary embodiments, the angles of taper A1 and A2 of theplugs 2131 and plug holes 2140 respectively may be between 30 and 90degrees, and more preferably between 60 and 90 degrees. The angles oftaper A1 and A2 may be about 82 degrees (+/−3 degrees to account forfabrication tolerances) as one non-limiting example. Other suitabletaper angles may be used.

When the impact limiter plugs 2131 are securely embedded in andfrictionally engaged with the plug holes 2140 such that the plugs areretained and cannot easily be removed by hand (see, e.g. FIG. 39B), theupper portions of the plugs protrude upward above the top surface 2105of the cask bottom closure plate 2103 as shown. Top surfaces 2132 of theplugs 2131 are therefore elevated above the closure plate 2103 formingplateaus or pedestals which collectively act as a seating surface toengage and support the bottom baseplate 2122 of the canister 2120 in araised manner elevated above the top surface of the bottom closureplate. When the canister is positioned on the plugs 2131, the canisteris therefore spaced apart from the bottom closure plate 2103 (i.e. topsurface 2105 thereof) by a vertical space or gap G (see, e.g. 34B). Thegap G advantageously provides a buffer or cushion zone allowing thecanister to gradually move downwards in the cask 2100 as the plugs 2131elastoplastically deform while moving deeper into the plug holes underthe kinetic impact forces generated by the cask striking a hard surfaceduring a drop event (see, e.g. FIG. 31 ). The impact limiter plugs 2131deform and progress deeper in plug holes 2140 due to the resultantimpact forces (i.e. canister against the plugs) to decelerate thecanister motion and reduce the g-load which protects the canister 2120and fuel assemblies therein. This is demonstrated in the test exampledescribed further below.

FIG. 39A shows a single impact limiter plug 2131 positioned above andready for insertion/embedment in its mating plug hole 2140. To installthe plug, the plug is loosely inserted and then partially driven intothe plug hole by a striking device such as a hammer or other deviceuntil the plug becomes snuggly fitted in and frictionally engaged withthe sidewalls 2143 of the hole. This eliminates looseness of the plugswhile the canister 2120 is loaded into the cask 2100. The frictionallyand mutually engaged tapers of the sides 2134 of plugs 2131 and plughole sidewalls 2143 thus retain the fitted plugs in the holes via afriction fit. The plugs therefore are not loosely placed in the plugholes, but rather cannot be removed by hand when properly installed. Theplugs are now partially embedded in their respective plug holes as shownin FIG. 39B and ready for service to receive and seat the canister 2120thereon when loaded into the cask 2100. In this pre-impact positionshown, the bottom surface 2133 of plug 2131 is spaced vertically apartfrom the bottom surface 2144 of the plug hole 2140. This provides spacefor the plug to move deeper into the plug hole as the plug is forcedinwards into the hole as it undergoes elastoplastic deformation due toimpact forces generated by the drop event.

In the occurrence of a cask drop event (see, e.g. FIG. 31 ), the cask2100 falls vertically for a distance and may strike/impact a hardsurface such as that defined by a. concrete pad/slab 2115. This accidentmay occur if the cask rigging or hoist mechanism associated with atrack-driven cask crawler, which is commonly used in the industry forlifting/lowering and transporting the cask with fuel canister 2120therein, were to fail. However, other scenarios of dropping the cask, ordropping canister into the cask while loading it therein, are possibleas well. The bottom closure plate 2103 of the cask is the firstcontainment vessel to impact the immovable hard surface and decelerateto zero acceleration due to gravity. The momentum of the fallingcanister 2120 inside the cask 2103 resulting from the drop causes thecanister to continue its downward motion momentarily (e.g. fraction of asecond) until its movement is in turn fully arrested by engagement withthe impact limiter plug assemblies 2130 on the bottom closure plate 2103of cask 2100. The baseplate 2122 of the canister 2100 may remain engagedwith the impact limiter plugs 2131 during the fall or may slightly moveajar, depending on the height of the drop and relative weights of thecask and canister (cask typically being heavier due to its thicksidewalls which may include concrete for radiation shielding). In eitherevent, the impact force F (g-load/force) of the canister against theimpact limiter plugs 2131 illustrated in FIG. 39B causes the plugs tobecome driven deeper into their respective plug holes 2140 by overcomingthe interfacial frictionally engagement forces between the sides 2134 ofthe plugs and corresponding hole sidewalls 2143 and elastoplasticdeformation of the metallic plugs. This deeper second position of theplugs 2131 in the holes 2140 is shown in FIG. 39C. In this figure, thebottom surfaces 2133 of the now more deeply embedded plugs after impact(“post-impact position) are separated from the bottom surface 2144 ofthe plug holes by a lesser distance or space by comparison than the“pre-impact” plug position shown in FIG. 39B. Similarly, the tops of theimpact limiter plugs may still protrude upward beyond the top surface2105 of the cask bottom closure plate 2103, but also by a lesser amountor distance than pre-impact. In some impact events scenarios andembodiments, the tops of the plugs may be driven completely flush withthe top surface of the bottom closure plate.

Due to the impact of the falling cask scenario (drop event), the plugs2131 concomitantly undergo some degree of elastoplastic deformation asthey are driven deeper into their respective plug holes 2140. In somecases depending on the angles of tapers A1, A2 and sizes used for theplugs and holes, and other parameters such as the metal materialselected for the plugs versus the cask bottom closure plate 2103, theplugs may possibly contact the bottom surface 2144 of the holesdepending on the magnitude of the kinetic impact force (which equates tothe height of drop). In some instances, the tops of the plugs maypossibly deform and mushroom due to the impact force which may reducethe penetration depth of the plugs in the holes. In either case, thedeformation and frictional engagement of the plugs 2131 with thesidewalls 2143 of the plug holes 2140 absorbs at least some of theimpact force and causes the canister 2120 to more gradually decelerate,thereby decreasing the g-load imparted on the canister to better protectthe structural integrity of the canister and fuel assemblies storedtherein. In sum, under impact, the tapered plugs 2131 would advanceinside the tapered holes 2140 as the kinetic impact energy is dissipatedby the combined action of interfacial friction therebetween and theelastic/plastic expansion action or deformation of the plugs in the plugholes.

The principal engineering parameters of the impact amelioration systemsuch as the material selected for the tapered impact limiter plugs 2131in contrast to the cask bottom closure plate 2103 which defining thecorresponding plug holes 2140, angle of taper A1 and A2 of the plugs andholes, plug diameter, and the number and pattern/arrangement of plugs onthe bottom closure plate make possible to decrease the peak g-loadimparted to the canister 2120 during a cask drop event significantly.

In one non-limiting arrangement, a first group or cluster of impactlimiter plug assemblies 2130 (pairs of tapered plugs 2131 and matingplug holes 2140) may be arranged in a circular array on the bottomclosure plate 2103 of the cask 2100 (see, e.g. FIGS. 33-34 and 37-38 ).The plug assemblies are circumferentially spaced apart as shown.Depending on the diameter D1 of the plugs 2131, additional circulararrays may be added inside and/or outside of the array shown. In someembodiments, one or more a center plug assemblies 2130 may be locatedcentrally with respect to and inside of the circular array. A singleplug assembly located at and intersecting the vertical centerline \′c ofthe canister may be provided in some embodiments. In other embodiments,a cluster of center plug assemblies 2130 may be provided and arranged inany suitable pattern within the outer circular array of assemblies. Theplug assemblies 2130 are located within the recessed canister seatingarea 2108 of the cask bottom closure plate 2103 inside the raise annularbottom ring plate 2106 as shown. This is the area which receives thebottom baseplate 2122 of the fuel canister 2120.

In other less preferred but possible embodiments contemplated, thearrangement of the plug assemblies 2130 may be reversed to that shown.Accordingly, the plug holes 2140 may be downward facing openings formedin the base plate 2122 of canister 2120 provided if the base plate issufficiently thick. The tapered the plugs 2131 may be embedded in theholes and protrude downwards from the base plate to engage the topsurface of the cask bottom closure plate 2103 when the canister isloaded therein.

Test Example

To demonstrate the impact amelioration system concept, the case of afalling transfer cask 2100 containing an MPC (canister 2120) isconsidered with reference to FIG. 31 . The transfer cask is assumed tofall from a height of 6.56 feet in this postulated scenario onto areinforced concrete pad or slab 2115. The following data characterizesthe physical/mechanical parameters of the computer simulated drop test:weight of transfer cask 2100 body: 120,000 pounds; weight of the loadedMPC 2120: 90,000 pounds; MPC diameter 75¾ inches; thickness of thetransfer cask baseplate 2103: 5½ inches; Material of impact limiter rodor plug: ASME/ASTM SA479 stainless steel; Material of cask bottomclosure plate 2103: ASME/ASTM SA516 Grade 70.

Calculations using LS-DYNA (a state-of-the-art impact dynamics codewidely used in the industry) showed the peak deceleration of the MPC tobe 262 g's when the transfer cask is dropped with the MPC restingdirectly onto the transfer cask baseplate without impact limiterassemblies 2130. Next, using the present impact amelioration systemdisclosed herein, the cask's bottom closure plate 2103 was equipped with16 circumferentially arranged impact limiting plugs 2131 of 4-inchdiameter (D1) and 82 degree included angle of taper (A1) each situatedin frustoconical plug holes 2140 also with 82 degree included angle oftaper (A2). An equal sized impactor at the centerline Vc of the MPC 2120was also employed. When this second configuration with impact limiterassemblies 2130 was employed, the peak deceleration of the MPC droppeddown to 180 g's. The impact limiter plugs 2131 were driven into andadvanced in the holes by only 0.13 inch to achieve this substantialreduction in g-load. Therefore, by reducing the angle of taper in otherconfigurations, the penetration of the plugs 2131 into the plug holes2140 can be further increased, and the g-load correspondingly reducedfurther. Accordingly, the foregoing analysis demonstrates the benefitsof present impact amelioration system for reducing the g-load on thecanister and protecting the canister and fuel assemblies stored therein.

FIGS. 40 and 41 show an alternate embodiment of an impact limiterassembly. In this embodiment, the plug hole 2150 includes an uppertapered portion 2150 a similar to that previous described herein whichis frustoconical shaped. The adjoining lower portion 2150 b of the plugholes 2150 comprises sacrificial threads configured to deform undershear forces imparted by the plugs 2131 when the plugs are driven deeperinto the plug holes under impact during a cask drop event. The plugs2131 have a mating threaded bottom extension 2131 a engaged with thethreaded hole. Shearing of the threads as the plug 2131 is driven deeperinto the plug hole 2150 after a cask drop event serves to extract impactenergy from the fall. The deformation of sacrificial threads inconjunction with the frictional forces acting between the plug and holesidewalls mutually contribute and act in unison to absorb the g-forcesacting on the canister 2100 during the drop event. The threaded lowerportion 2150 b of the plug holes 2150 may extend complete through thebottom surface of the cask bottom closure plate 2103, or in otherembodiments may have a closes bottom which does not penetrate the bottomsurface of the closure plate. Either embodiment may be used. It bearsnoting that the threaded impact limiter plugs 2131 also facilitateinstallation of the plugs by simply rotating the plugs to threadablyengage the threaded plug holes 2150, thereby retaining the plugs untilthe canister 2120 is loaded into the transfer cask 2100.

FIGS. 42 and 43 show yet another embodiment of an impact limiterassembly. In this embodiment, the plug hole 2160 has straight sidewalls2161 and a closed bottom. An annular expansion ring 2170 is seated inplug hole 2160. Expansion ring 2170 includes straight exterior sides2170 a and a vertical tapered central opening 2171 of frustoconicalshape which may extend completely through the ring as shown. The opening2171 defines corresponding frustoconical walls which may becomplementary configured in angle of taper to the angle of taper A1 ofthe plug 2131. The top surface of the expansion ring 2170 may berecessed within in plug hole 2160 below the top surface 2105 of the caskbottom closure plate 2103 as shown.

In this present embodiment of FIGS. 42 and 43 , impact limiter plug 2131retains a frustoconical shaped central portion 2135 but adds a radiallyprotruding peripheral flange 2133 at the top of the plug as shown. Theplug with flange may have a diameter measured at its top surface(similar to diameter D1) which in this case is smaller than the topopening of the plug hole 2160 such that the flange can at least enterthe plug hole 2160 as shown. The central portion 2135 of plug 2131 stillfrictionally engages the central opening 2171 of the expansion ring 2170to retain the plug in place in the pre-impact position shown.Preferably, the expansion ring 2170 is sized in outer diameter so that asmall annular space is formed between the sides of the ring and thesidewalls 2161 of plug hole 2160. This provides room for the ring 2170to expand under impact forces after a cask drop event.

In operation after the cask 2100 is dropped, the impact limiter plug2131 is driven deeper into tapered central opening 2171. The impactforce F acting on the mating tapered/angled surfaces of the plug andexpansion ring 2170 within the central opening 2171 has alateral/horizontal force component (in additional to a vertical forcecomponent) as well understood by those skilled in the art. Thehorizontally acting force component deforms and expands the ringradially outwards as it is squeezed between the plug 2131 and plug hole2160 to close the annular space between the ring and plug hole 2160sidewalls 2161. In some instances, the ring may possibly engage thesidewalls 2161 as it radially expands. The expansion ring in combinationwith mating tapered surfaces of the impact limiter plug 2131 andexpansion ring 2170 act in unison to absorb and reduce the g-loadimparted to the canister 2120 during the cask drop event. The peripheralflange 2133 of plug 2131 may completely enter the plug hole 2160. FIG.43 shows the pre-impact position of the plug in the impact limiterassembly. Expansion ring 2170 may be formed of any suitable metallic ornon-metallic material. Preferably, the ring is formed of a materialhaving greater ductility (i.e. softer) than the plug 2131 to facilitatethe expansion of the ring. In one embodiment, the expansion ring 2170 isformed of metal such as steel or aluminum. In other embodiments, thering may be formed a non-metallic material such as a dense polymer.

In view of all the foregoing embodiments of an impact ameliorationsystem, the included taper angles of the tapered plugs 2131 and plugholes 2140, their material of construction and dimensions, number andarrangement/pattern of impact limiter assemblies 2130 on the cask bottomclosure lid 2130, number and type of threads used in the embodiment ofFIGS. 40-41 , the height/thickness and material of the optionalexpansion ring 2170 used in the embodiment of FIGS. 42-43 , and otheraspects are among the parameters that can be varied to obtain theoptimal energy extraction for a specific impact scenario to protect thecanister 2120 and its waste fuel contents from severe damage.

The impact limiter plugs 2131 can generally advance in the holeprimarily by expanding/deforming the plugs in an elastoplastic mannerwhich exceeds the yield stress of the material, and by overcoming thefriction at the tapered/angled interface between the plug and matingplug holes. The plugs are therefore preferably formed of a metallicelastoplastic material such as without limitation steel which undergoeselastic and plastic deformation when the load/force exceeds the yieldstress of the material. Plastic deformation beyond the yield stressconnotes that the plug will retain permanent deformation and not returnto its original condition (e.g. shape and dimensions). Depending on thematerial selected for the cask bottom closure plate 2103, the sidewallsof the plug holes may similarly undergo elastic-plastic deformation toabsorb some of the kinetic impact energy resulting from a cask dropevent.

Third Inventive Concept

Unventilated Cask for Storing Nuclear Waste

Reference is made generally to FIGS. 45-60 which are relevant to theThird Inventive Concept described below.

FIGS. 45-60 show various aspects of the nuclear fuel storage systemcomprising an unventilated nuclear fuel storage pressure vessel with aself-regulating pressure relief mechanism and integral heat dissipationsystem. The nuclear fuel storage system in one embodiment generallycomprises a pressure vessel in the form of an outer unventilated storagecask 3100 and a high level radioactive nuclear waste (e.g., SNF)canister 3120 configured for storage inside the cask. Features of eachstorage vessel and other features thereof will now be further described.

Canister 3120 may be used for storing any type of high level radioactivenuclear waste, including without limitation spent nuclear fuel (SNF) orother forms of radioactive waste materials removed from the reactor. TheSNF or simply fuel canister for short may be any commercially-availablenuclear waste fuel canister, such as a multi-purpose canister (MPC)available from Holtec International of Camden, N.J. or other.

Referring momentarily to FIG. 57 , waste fuel canister 3120 has avertically elongated and metallic body comprised of a cylindrical shell3121. Canister 3120 further includes a bottom baseplate 3122 seal weldedto a bottom end of the shell, and an open top closed by an attached lid3125. Lid 3125 may be seal welded to a top end 3126 of the canistershell 3121 to form a hermetically sealed cavity 3127 inside thecanister. The foregoing canister parts may be formed of any suitablemetal, such as for example without limitation steel including preferablystainless steel for corrosion protection.

Fuel basket 3123 is disposed in cavity 3127 of the canister 3120 and isseated on the bottom baseplate 3122 as shown. The fuel basket may bewelded to the baseplate for stability in some embodiments. In someembodiments, the baseplate 3122 may extend laterally outwards beyond thesides of the fuel basket 3123 around the entire perimeter of the fuelbasket as shown.

The fuel basket 3123 is a honeycomb prismatic structure comprising anarray of vertically-extending openings forming a plurality of verticallongitudinally-extending fuel assembly storage cells 3124. Each cell isconfigured in cross-sectional area and shape to hold a single U.S. stylefuel assembly, which contains multitude of spent nuclear fuel rods (orother nuclear waste). An example of fuel assembly of this type having aconventional rectilinear cross-sectional configuration is shown in FIG.58 of U.S. patent application Ser. No. 17/132,102 filed Dec. 23, 2020,which is incorporated herein by reference. Such fuel assemblies and theforegoing fuel basket structure are well known in the industry. The fuelbasket may be formed in various embodiments by a plurality ofinterlocked and orthogonally arranged slotted plates built up to aselected height in vertically stacked tiers. Other constructions of fuelbaskets such as via joining multiple vertically extending tubes or otherstructures to the canister baseplate may be used and others used in theart may be used. The fuel basket construction is not limiting of thepresent invention.

With continuing reference to FIGS. 45-60 , the unventilated storage cask3100 in one embodiment is a double-walled pressure vessel comprising avertically elongated metallic cylindrical body 3100 a defining avertical longitudinal axis LA passing through the vertical centerlineand geometric center of the body. The cask body is an annular structureincluding an outer shell 3101, an inner shell 3102 spaced radiallyinwards therefrom and defining an annular space 3106 between the shells,a circular bottom baseplate 3103 coupled to the bottom ends of theshells, and an annular top closure plate 3104 coupled to the top ends ofthe shells. The shells are arranged coaxially relative to one another.Baseplate 3103 may be fixedly attached to the top and bottom ends of theshells preferably by via seal welding to form a hermetic bottom seal ofthe cask body. Accordingly, continuous circumferential seal welds maypreferably be used to permanently join the bottom baseplate 3103 to theshells 3101, 3102.

The circumferential outer edge 3104 b of top closure plate 3104 may bewelded to a top end of the outer shell 3101 of the cask 3100. The topclosure plate has a radially broadened ring-like plate structure whichprojects radially inwards from the outer shell towards the inner shell3102. In one embodiment, as shown, top closure plate 3104 projectsradially inwards towards but does not contact or engage the inner shell3102 of the cask 3100 to partially close the annular space 3106 at topbetween the shells of the cask body. This arrangement providesadditional space for a pressure release/relief passageway to quicklyrelease excess pressure from the cask in the event of an internal caskoverpressurization condition, as further described herein.

With particular emphasis on FIGS. 54 and 59-60 , the top closure plate3104 of cask 3100 comprises a plurality of fastener holes 3109 whichreceive bolt assemblies 3140 therethrough to threadably engagecircumferentially spaced anchor bosses 3165 fixedly mounted to the topend of the cask body 3100 a, as further described herein. Fastener holes3109 are circumferentially spaced apart along a bolt circle of suitablediameter. In one embodiment, fastener holes 3109 may be circular andformed through an annular recessed gasket seating surface 3110 formed onthe inner annular portion of the top closure plate 3104. The raisedouter annular portion 3113 of the top closure plate may be flat andplain as shown without openings. A compressible annular gasket 3111containing circumferentially spaced apart circular fastener apertures3112 is received on gasket seating surface 3110. When mounted thereon,fastener apertures 3112 are concentrically alignable with fastener holes3109 of the cask top closure ring 3104. Gasket 3111 forms acircumferential hermetic seal between the lid 3150 and top closure plate3104 of the cask body 3100 a. Any suitable natural or man-madecompressible material (e.g., elastomeric, rubber, etc.) materialsuitable for the intended service conditions (e.g., temperature,pressure, environment, etc.) may be used.

The cask body 3100 a defines an internal cavity 3105 which extendslongitudinally for a full height of the cask from baseplate 3103 atbottom to the top ends of outer and inner shells 3101, 3102. The cavity3105 is configured in dimension and transverse cross-sectional area tohold only a single fuel canister 3120 in some embodiments, as isconventional practice in the art. Cavity 3105 is hermetically sealedwhen lid 3150 is mounted to the cask body 3100 a and may therefore bepressurized to pressures above atmospheric, thereby categorizing cask3100 as a pressure vessel for ASME code purposes. The stress field inthe cask's pressure retention boundary may be qualified to the limits ofSection III Subsection ND of the ASME Boiler and Pressure Vessel Code.

The cask 3100 is a heavy radiation shielded nuclear waste fuel storagepressure vessel operable to ameliorate the gamma and neutron radiationemitted by the nuclear waste fuel canister 3120 to safe levels outsidethe cask. Accordingly, annular space 3106 formed between outer and innershells 3101, 3102 is filled with appropriate radiation shieldingmaterial(s) 3107. In some embodiments, the shielding material 3110 maycomprise plain or reinforced concrete. Concrete densities up to 3230pounds/cubic feet or more may be used. However other or additionalshielding materials and combinations thereof may be used includingwithout limitation lead, boron-containing materials, or a combination ofthese and/or other materials effective to block and/or attenuate gammaand neutron radiation emitted by the nuclear waste (e.g., fuelassemblies) stored in canister 3120 when loaded into the cask 3100. Anysuitable types, thicknesses, and arrangement of shielding materials maybe used to provide the necessary degree of shielding.

The outer and inner shell members 3101, 3102 of the cask 3100 may beformed of a suitable metal such as for example without limitationpainted steel. The top closure plate 3104 and bottom baseplate 3103 maysimilarly be formed of the same metal for welding compatibility andstrength.

In one embodiment, a plurality of steel canister cross supports 3115 maybe welded to the top surface of the baseplate 3103 (see, e.g., FIG. 46 )inside internal cavity 3105 to support the canister 3120. The crosssupports elevate the bottom of the canister above the baseplate. Crosssupports 3115 may be arranged in an intersecting X-pattern (cruciform)as shown; however, other suitable arrangements of the supports may beprovided. In certain embodiments, a plurality of circumferentiallyspaced apart metallic seismic restraint tubes 3116 may be welded to theinterior surface of inner shell 3102 inside cavity 3105. The tubes keepthe canister 3120 centered and reduce radial/lateral movement duringoccurrence of a seismic event. A grouping of restraint tubes 3116 may beprovided in both the upper and lower portion of cask cavity 3105 torestrain the top and bottom portions of the canister 3120.

In contrast to vertical ventilated overpacks or casks, it bears notingthat the present unventilated cask 3100 has no provisions which allowfor the exchange of ambient cooling air through the internal cavity 3105of the cask to cool the canister by natural thermo-siphon convectiveairflow. As previously noted herein, such ventilated cask designs may beunsuitable for storage of spent nuclear fuel (SNF) in a stainless steelcanister within the cask in corrosive atmospheric environments andconditions. Many SNF canisters are made of austenitic stainless steel,which is susceptible to stress corrosion cracking (SCC) in humidcorrosive environments in the presence of residual tensile surfacestresses remaining from the fabrication of the canisters. In coastalenvironments, the presence of airborne salts can be especiallyproblematic and render a stainless steel SNF canister susceptible tochloride-induced SCC.

Because the internal cavity 3105 of the present unventilated cask 3100is gas-tight and forms a pressure vessel, a heat dissipation mechanismis necessary to cool the canister within this hermetically sealedstorage environment within the cask. In addition, further structuralreinforcement of the cask's skeletal steel structure is desired toenable safe lift and transport of the cask with a motorized cask crawlerin view of the heavy concrete laden cask body which can readily weightin excess of 3100 tons.

To provide both additional structural strength to the cask and a heattransfer mechanism to cool the nuclear waste fuel canister 3100 in cask3100, the cask may include a plurality of longitudinally-extending ribplates 3160. FIG. 58 shows one form of rib plate 3160 a in isolation andgreater detail which contains lid mounting bosses 3165. Plain rib plateshave a similar construction minus the mounting bosses, as furtherdescribed below.

With continuing general reference to FIGS. 45-60 , the longitudinal ribplates 3160 are flat sheet-like rectangular structures disposed insideannular space 3106 of cask 3100 between the inner and outer shells 3102,3101. The ribs plates are circumferentially spaced apart and weldedalong opposing longitudinal edges 3161 of the plates to at least theinner and outer shells 3102, 3101. In one embodiment, longitudinallycontinuous fillet welds may be used which extend along the entire heightof the rib plate to shells joint Rib plates 3160 further include a topedge 3162, bottom edge 3163, and opposed flat and parallel majorsurfaces 3164. The rib plates extend radially between the inner andouter shells 3102, 3101, and in some embodiments may be arranged indiametrically opposed pairs of plates (see, e.g., FIG. 53 ). Rib plates3160 extend for a full longitudinal height of the annular space 3106 ofthe cask from the baseplate 3103 to a top end of the cask body at thebottom surface of the top closure plate 3104 (see, e.g., FIGS. 46A-B,48, and 49A). In certain embodiments, the rib plates 3160 may be weldedat their top and bottom edges 3162, 3163 to the baseplate 3103 and/ortop closure plate 3104 to further strengthen the cask skeletalstructure. The circumferential gaps formed between rib plates 3160within the annular space 3106 are filled with the radiation shieldingmaterial 3107, such as without limitation concrete.

It bears noting that the rib plates 3160 each provide a conductive heattransfer path between the inner shell 3102 and outer shell 3101. Theinterior surface of inner shell 3102 is heated by direct exposure to thewaste fuel canister 3120. The heat flows radially outward through therib plates 3160 via conduction to heat the outer shell 3101, which thenbecomes hot and dissipates heat to the atmosphere via convective coolingand radiation.

Some of the rib plates 3160 are configured to act as load transfermembers used in lifting the cask 3100. Accordingly, lifting rib plates3160 a each comprise a threaded anchor boss 3165 fixedly attached at atop end thereof (see, e.g., FIG. 58 ). Anchor boss 3165 comprises acylindrical body defining an upwardly open threaded bore 3166 positionedto threadably engage a respective mounting bolt 3140. assembly. The topof the mounting boss may be flush with the top edge 3162 of the liftingrib plate in some embodiments as shown which allows the height of therib plate to be maximized, which in turn maximizes its heat transfercapacity. A plurality of lifting rib plates 3160 a are preferablyprovided and spaced apart in circumferentially around the top end of thecask body. In the non-limiting illustrated embodiment, four lifting ribplates 3160 a are provided spaced 90 degrees apart around the cask bodyas shown (see, e.g., FIG. 53 ); however, a greater or few number may beprovided in other implementations of the cask. The lifting rib plates3160 a provide a load transfer interface with the lid 3150.

Lid 3150 is a radiation shielding structure with outer metallic casing(e.g., steel) comprising a circular top plate 3151, opposing circularbottom plate 3152, and a cylindrical outer lid shell 3153 welded to thetop plate and the bottom plate of the lid forming an internal cavity3154. Cavity 3154 is filled with radiation shielding material 3107,which may comprise concrete in some embodiments. Various other shieldingmaterials and combinations thereof may be used as previously describedherein with respect to the cask radiation shielding.

Lid 3150 further comprises a plurality of radially/laterally elongatedlid lifting plates 3155, which may be arranged in an orthogonalcruciform pattern intersecting at the center of the lid (see, e.g.,FIGS. 54, 59, and 60 ). The lifting plates are embedded in the concretefill and comprise a lifting lug 3156 protruding upwards beyond the topplate 3151. Lifting lugs 3156 are configured with holes for rigging toan overhead hoist or crane for raising, lowering, and transporting theunventilated storage cask 3100. Accordingly, lifting plates 3155 may bewelded to the top plate 3151, bottom plate 3152, and/or outer shell 3153to provide a rigid skeletal frame for the lid 3150 capable of handlingthe cask 3100 which generally weights in excess of 3100 tons.

Importantly, the lifting plates 3155 and the foregoing welded lidconstruction further act as a heat transfer mechanism to dissipate heatemitted by the canister 3120 in the cask cavity 3105 through the lid tothe ambient environment. To further enhance heat transfer, the liftingplates may penetrate the bottom plate 3152 of lid 3150 for directexposure to the cask cavity 3105 (see, e.g. FIG. 59 ). Lifting platesmay protrude downwards below the bottom surface of the bottom lid platein some embodiments as shown for this purpose and also to verticalstabilize the canister 3120 within the cask against vertical movementeither during transport of the cask or a seismic event.

By virtue of the thermosiphon effect occurring inside the waste fuelcanister 3120 (e.g., MPC) through the fuel basket 3123, the top lid 3125of the canister seen in FIG. 57 is the hottest part of the canister'sexterior surface. The hot canister heated by heat emitted by thedecaying spent fuel assemblies therein rejects heat to the bottom plate3152 of the cask's closure lid 3150 directly above and proximate to thetop of the canister by direct radiation and convection. The lid liftingplates 3155 and the physical connectivity they provide between thebottom plate 3152 and top plate 3151 of the lid directly exposed to theambient environment thus are important to the cask's thermal performancefor cooling the canister. From a personnel safety standpoint, having thehottest surface of the cask (i.e., lid 3150) located at the very top ofthe cask (away from the reach of surveillance personnel) is anadvantageous operational feature of the nuclear waste fuel storagesystem.

Referring specifically to FIGS. 49B and 60 , bottom plate 3152 of thelid 3150 comprises a plurality of circumference lid fastener holes 3157arranged to be concentrically aligned with fastener holes 3109 of casktop closure plate 3104 and threaded bosses 3165 of lifting rib plates3160 a. Each lid fastener hole 3157 is accessible through a respectiveaccess tube 3159 welded to bottom plate 3152. Access tubes 3159 projectupwards passing through lid top plate 3151, and preferably protrudingbeyond and above the top plate as shown to prevent the ingress ofstanding water from the top surface of the lid into the tube. The accesstubes are formed of steel, preferably stainless steel to preventcorrosion and accumulation of rust which might adversely affect thesliding motion of the floating lid along the bolt assemblies 3140 (e.g.,the threaded studs 3141). The tubes 3159 be further be welded to the topplate 51 in some embodiments. Access tubes 3159 are embedded in theconcrete radiation shielding material in the lid 3150 (see, e.g., FIGS.49A and 60 ).

For cask lid constructions where the bottom closure plate may be formedof steel which may corrode and rust, an annular hole insert plate 3158may optionally be used which is formed of stainless steel similarly tothe bolting assembly access tubes 3159. The hole insert plate is weldedpartially or fully around its circumference to the lid bottom plate toeliminate any pressure passage into the interior of the lid. Thefastener holes 3157 of lid 3150 in this case are formed by the holeinsert plates. In other embodiments, however, the insert plates 3158 maybe omitted and fastener holes 3157 may be formed directly in the lidbottom plate 3152 within the access tubes 3159. Either construction maybe used. The use of stainless steel to construct the access tubes 3159,hole insert plates 3158, and preferably the bolting assembly 3140components mitigates the formation of rust which might interfere withsmooth sliding movement of the floating lid 3150 along the boltassemblies during cask overpressurization conditions. This is anexposure since rainwater will tend to accumulate inside the access tubes3159 until the heat dissipated through the lid 3150 from the internalcavity 3107 of cask 3100 eventually evaporates the water.

Referring to FIGS. 49A-C and 59-60, the threaded bolt assemblies 3140each include a cylindrical threaded stud 3141 threadably engageable withthe anchor bosses 3165 (i.e., threaded bore 3166) of the lifting ribplates 3160 through the top closure plate 3104 of the cask 3100, aninternally threaded adjustable limit stop 3142 rotatably coupled to thestud for upward/downward positioning thereon, and optionally a washer3143 which receives the stud. In one embodiment, the limits stop 3142may be a threaded hex nut adjustable in position along the threaded studto change a height of an installer-adjustable vertical travel gap Gformed between the limit stop and bottom plate 3152 of the lid 3150.Where the optional washer 3143 is provided, travel gap G is formedbetween the top of the washer and the bottom surface of the lid bottomplate. Travel gap G defines a range of vertical travel of the lid alongstud 3141. In some embodiments, travel gap G may be about ⅜ inch ormore. Even such a small gap between the lid when raised and the caskbody is effective to relieve excess internal pressure from the cask.Accordingly, lid 3150 is vertically movable relative to the cask bodywithin a range defined by the travel gap. The forgoing bolt assemblycomponents (stud, limit stop, and washer) are preferably formed ofstainless steel to prevent corrosion and rust formation on the threadedstud 3141 which might inhibit the lid from freely sliding along thestuds when rising during a cask overpressurization condition.

To provide a self-regulating cask overpressurization relief system, theradiation shielding lid 3150 is a free-floating design which is movablycoupled to the top end of the cask 3100 in a hermetically sealablemanner by bolt assemblies 3140. Accordingly, the bolt assemblies 3140are configured to loosely mount the lid to the cask body, therebyallowing limited vertical movement of the lid relative to the cask bodyvia the foregoing installer-positionable limit stops 3142 of the boltassemblies to adjust the travel gap G. The weight of the lid acts inconjunction with the annular compressible gasket 3111 which forms acircumferential seal between the lid and the top end of the cask body tomaintain a hermetic seal of the cask body. This forms the gas tightcavity 3105 which houses canister 3120 under normal cask operatingpressures. The cask 3100 is therefore operable to retain an internalpressure within the gas tight cavity 3105 above atmospheric pressure.When the internal pressure P of the cask acting on the bottom surfacearea of the lid bottom plate 3152 exposed to the cask cavity 3105, thiscreates an upward acting lifting force which exceeds the weight of thelid, the lid will rise and become slightly ajar from the top closureplate 3104 of the cask to relieve the cask excess pressure (see, e.g.,FIG. 49B).

Lid 3150 may further comprise a metallic raised annular shear ring 3170protruding downwardly from a bottom surface of the lid bottom plate3152. The shear ring is designed such that if the cask 3100 tips over,the lid will contact the cask body top plate 3104 to absorb the shearforces instead of the bolt assemblies 3140. This protects the structuralintegrity and lid-to-cask seal of the cask cavity 3105. Shear ring 3170is arranged proximate to a circumferential inner edge 3104 a of the topclosure plate 3140 as shown in FIG. 49A for mutual engagementtherebetween in the event of a cask tipping event.

Lid 3150 is slideably movable in a vertical direction by a limitedamount along the bolt assemblies 3140 (i.e., threaded stud 3141particularly) dictated by travel gap G. Lid 3150 is movable between: (1)a downward sealed position engaged with the cask body which seals thegas tight cavity of the cask (see, e.g., FIG. 49A); and (2) anadjustable raised relief position engaged with the bolt assemblies butajar from the cask body to partially open the gas tight cavity therebydefining a gas overpressurization relief passageway to ambientatmosphere extending circumferentially and perimetrically around the topend of the cask body (FIG. 49B).

When an internal cask overpressurization condition occurs, the lid 3150rises under pressure P to close the travel gap G and engage the threadedlimit stop 3142 on stud 3141 with the bottom plate 3152 of the lid whicharrests upward movement of the lid. The heating of the trapped volume ofgas in the cask cavity 3105 (i.e., air or an inert gas pumped into thecask cavity after placement of and sealing by the lid) by the fuelassemblies stored within the SNF canister 3120 will on its own cause anincrease in internal cask pressure P to the point limited by the weightof the free-floating lid. Such an overpressurization condition may alsobe associated with spent nuclear fuel dry storage system (i.e., cask)Design Basis Fire Event, or other abnormal operating condition withinthe cask. The U.S. NRC (Nuclear Regulatory Commission) mandates drystorage systems to meet stringent safety requirements at all times,including during the occurrence of postulated cask design basis accidentevents. A design basis accident is any event that could significantlyaffect the integrity of the storage system, such as an external fire,fuel rod rupture, and natural phenomena such as earthquakes, lightningstrikes, projectile impacts, and others.

When the cask overpressurization condition abates, the relieved internalcask pressure drops back down within the cask and lid 3150 automaticallyreturns to the downward position under its own weight to re-engage thecask body and reseal the gas tight hermetically sealed cavity 3105. Inthe event an overpressurization condition occurs again, the lid 3150will again rise to relieve the excess pressure and repeat the cyclewithout manual intervention, thereby forming a self-regulating caskoverpressurization relief system.

In view of the foregoing, a method or process for protecting anunventilated nuclear fuel storage cask from internal overpressurizationwill now be briefly summarized. The method includes providing theunventilated cask 3100 comprising the sealable internal cavity 3105 anda plurality of threaded anchor bosses 3165. The cavity of the caskremains upwardly open at this juncture. The method continues withlowering canister 3120 containing high level nuclear waste into thecavity 3105, and then positioning the radiation shielded lid 3150 on thecask. The lid is now in the downward sealed position engaged with thecask thereby making the cavity gas tight to retain pressures exceedingatmospheric. The method continues with aligning the plurality offastener holes 3109 formed in the lid 3150 (e.g., in lid bottom plate3152) with the anchor bosses. Next, the method includes threadablyengaging a threaded stud 3141 of the bolt assemblies 3140 with each ofthe cask anchor bosses 3165 through the fastener holes 3109 of the lid,and then rotatably engaging a threaded limit stop 3142 with each of thethreaded studs. This last step may be preceded by sliding a washer 3143over each threaded stud 3141 to rest on the lid (e.g., lid bottom plate3152 at the base of access tubes 3159) if washers are optionally used.The final step comprises rotating and positioning the limits stops 3142on the studs 3141 such that a vertical travel gap G is formed betweenthe lid and the limit stops. This position of the lid 3150 is shown inFIG. 49A. During a cask overpressurization condition wherein the upwardforce exerted on the bottom surface of the free-floating lid 3150 by theinternal pressure of the cask exceeds the weight of the lid, the lidslideably moves upward along the studs 3141 to the relief position ajarfrom the cask to vent excess pressure to atmosphere. As previouslydescribed herein, when the cask overpressurization condition abates, thelid automatically returns to the downward position to re-engage the caskbody and reseal the gas tight cavity for continued operation.

In some embodiments, the pressure of the cask cavity 3105 which holdsthe waste fuel canister 3120 air may be reduced to a low enough valuesuch that it will remain below the ambient pressure under all serviceconditions. To ensure that the cask operates under sub-atmosphericconditions, it would be necessary to pump out the ambient air in thecask cavity 3105 after the canister 3120 and lid 3150 are in place.Typically, an initial pressure of about ½ atmosphere would generally besufficient to ensure that the internal pressure of the cask 3100 remainssub-atmospheric under all operating conditions. Suitable pipingconnections and valving may be provided to pump the air out of the caskand establish the sub-atmospheric cask operating pressure. The caskcavity 3105 may next be optionally filled with an inert gas aftermounting the lid 3150 tot the cask 3100 in some embodiments. This addedsafety measure to protect the long term integrity of the canisterconfinement barrier may be used where the onset of SCC at the exteriorsurfaces of the canister 3120 may be an operational issue.

Fourth Inventive Concept

Storage and Transport Cask for Nuclear Waste

Reference is made generally to FIGS. 61-92 which are relevant to theFourth Inventive Concept described below.

FIGS. 61-88 show various aspects of the nuclear waste transport andstorage system. The system includes nuclear waste transfer and storagecask 4100 (hereafter nuclear waste cask for brevity) which is usabletransport and/or store high level nuclear waste materials. Cask 4100comprises an elongated rectilinear-shaped cask body 4101 defining alongitudinal axis LA and the lower part of the containment barrier forthe nuclear waste. The body 4101 may have a rectangular cuboidconfiguration in one embodiment (as shown) comprising an axiallyelongated bottom wall 4102, a parallel pair of longitudinal sidewalls4103 attached to the bottom wall, and a pair of lateral end walls 4104attached to opposite ends of the bottom wall between the sidewalls. Thelongitudinal sidewalls are attached to the longitudinal sides or edgesof the bottom wall. End walls 4104 are oriented transversely andperpendicularly to longitudinal axis LA and longitudinal sidewalls 4103,and the longitudinal sidewalk are oriented parallel to the axis to formthe box-like structure shown. In one embodiment, the sidewalls and endwalls may be welded to each other and in turn to the bottom wall to forma weldment. Four corners 4107 are formed at the intersection of thesidewalls 4103 and end walls 4104 which extend vertically along theheight of the cask body 4101.

Bottom wall 4102 has a flat top surface 4102 a and parallel opposingflat bottom surface 4102 b. The bottom wall is configured to be seatedon a horizontal support surface such as a concrete pad. The interior andexterior surfaces of each of the longitudinal sidewalls 4103 and endwalls 4104 may be generally flat and parallel to each other as well.

Cask 4100 may be used in horizontal position as shown when transportingand storing nuclear waste. In this case, the vertical direction isdefined for convenience of reference as being transverse andperpendicular to the longitudinal axis LA. A lateral direction isdefined for convenience of reference in the horizontal direction asbeing transverse and perpendicular to the longitudinal axis.

The bottom wall 4102, longitudinal sidewalls 4103, and end walls 4104collectively define an internal storage cavity 4105 configured forstoring nuclear waste materials previously described herein. The bottomwall, longitudinal sidewalls, and end walls define and circumscribe anaxially elongated top opening 4106 forming an entrance to the cavity forloading nuclear waste materials therein. The longitudinally-extendingtop opening 4106 extends for a substantial majority of the entire lengthof the cask body (less the thicknesses of the sidewalls and end walls).This provides a large opening which facilitates loading many differentshapes and sizes nuclear waste materials into the cask 4100.

Longitudinal sidewalls 4103 and lateral end walls 4104 of the cask mayeach have a composite construction comprising a metallic innercontainment plate 4110 adjacent to the storage cavity 4105 and ametallic outer radiation dose blocker plate 4111 abutted thereto. Bottomwall. 4102 may similarly have a composite construction comprising ametallic inner containment plate 4112 adjacent to the storage cavity anda metallic outer radiation dose blocker plate 4113. In some embodiments,as shown, an intermediate dose blocker plate 4114 may be sandwichedbetween the inner containment plate and outer dose blocker plate whenneeded to provide additional radiation shielding. In some non-limitingembodiments, the containment plates may be formed of steel alloy and theradiation dose blocker plates may be formed of a different steelmaterial such as for example stainless steel for protection againstcorrosion by the exterior ambient environment. A suitable thickness ofthe containment and blocker plates may be used as needed to effectivelyreduce the radiation emitted from the cask to within regulatorycompliant exterior levels for containment casks. As noted, the bottomwall and walls of cask 4100 may have an all metal construction withoutuse of concrete. However, in other possible embodiments, concrete andadditional or other radiation shielding materials includingboron-containing materials for neutron attenuation and variouscombinations thereof may be provided if additional radiation blocking isneeded. The bottom wall and wall construction materials used thereforedo not limit the invention.

With continuing reference to FIGS. 61-88 , cask 4100 further includes alongitudinally elongated closure lid 4200 which forms the uppercontainment barrier. Lid 4200 may be of rectangular shape in oneembodiment to match the rectangular cuboid configuration of the caskbody 4101 shown. Lid 4200 has a length and width sufficient to form acomplete closure of the top opening of the cask in order to fullyenclose and seal the internal storage cavity 4105 of the cask andnuclear waste materials. Lid 4200 includes an outward facing top surface4201 and parallel bottom surface 4202 facing cavity 4105 of the caskbody 4101 when positioned thereon, parallel longitudinal sides 4203(i.e., long sides of the lid), parallel lateral ends 4204 (i.e., shortsides of the lid) extending between the longitudinal sides, and corners4205 (four as shown) at the intersection of the longitudinal sides andlateral ends. Top and bottom surfaces 4201, 4202 are the major surfacesof the lid having a greater surface area than other surfaces on the lid.

Referring additionally to FIGS. 70-77B, closure lid 4200 may have acomposite construction comprising a metallic inner containment plate4206 at bottom located adjacent to the storage cavity 4105 when the lidis position on the cask body 4101, and a top metallic outer radiationdose blocker plate 4207. Containment plate 4206 defines bottom surface4202 of the lid and blocker plate 4207 defines top surface 4201. Aninsulation board 4208 may be sandwiched between plates 4206 and 4207 forprotection against fire event.

In one embodiment, a peripheral lid spacer frame 4209 may be attached tothe bottom containment plate 4206 of lid 4200. Frame 4209 has an openspace-frame structure which extends perimetrically around the bottomsurface 4202 of the lid. The frame 4209 may include an X-brace 4209 aextending through the interior space defined by the peripheral linearmembers of the frame to add structural reinforcement and bracing. Whenlid 4200 is positioned on cask body 4101, inner containment plate 4206and frame 4209 are received completely into storage cavity 4105 of thecask (see, e.g., FIGS. 70 and 71 ).

A compressible gasket 4220 may be disposed on the bottom surface 4202 ofthe lid 4200 to form a gas-tight seal at the interface between the lidand cask body. Gasket 4220 has a continuous perimetrically extendingshape which is complementary configured dimensionally to conform to andcircumscribed the top end of the cask body 4101 on all sides. Gasket4220 therefore extends perimetrically along the tops of the longitudinalsidewalls 4103 and lateral end walls 4104 of the cask to form aneffective seal. Gasket 4220 may be formed of any suitable compressiblematerial, such as elastomeric materials in some embodiments.

According to one aspect of the disclosure, a bolt-free cask lockingmechanism provided to lock and seal lid 4200 to cask body 4101. FIGS.70-78 and 82-88 in particular show various aspects of the bolt-free casklocking mechanism, which will now be further described in detail.

Lid 4200 and cask body 4101 include a plurality of locking featureswhich cooperate to form the locking mechanism. The cask lockingmechanism may comprise a plurality of first locking protrusions 4212spaced apart on the lid which are selectively and mechanically,interlockable with a plurality of second locking protrusions 4214 spacedapart on the cask body to lock the lid to the cask body. First lockingprotrusions 4212 are movable relative to the lid and cask body 4101,whereas second locking protrusions 4214 are fixed in position on andstationary with respect to the cask body.

The locking features of the lid 4200 comprises at least one firstlocking member 4212 a, which may be in the form of a linearly elongatedlocking bar 4210 for locking the lid to the cask body (see, e.g., FIGS.75B and 89-92 ). In one embodiment, a plurality of elongated lockingbars 4210 are arranged perimetrically around the outer peripheralportions of the lid on longitudinal sides 4203 and lateral ends 4204.First locking protrusions 4212 are formed on and may be an integralunitary structural part of the locking bars in one embodiment beingformed of single monolithic piece of cast or forged metal. In otherpossible less preferred but satisfactory embodiments, lockingprotrusions 4212 may be discrete elements separately attached to thelocking bars 4210 via mechanical fasteners or welding.

Locking bars 4210 are slideably disposed in corresponding outward facingelongated linear guide channels 4211 formed in the longitudinal sidesand lateral ends of the lid 4200. The locking bars are movable back andforth in opposing directions within the guide channels relative to thelid. Each locking bar 4210 includes a plurality of the first lockingprotrusions 4212 which project outwardly from the bar beyond the outwardfacing surfaces of the longitudinal sides 4203 and lateral ends 4204 ofthe lid. The linear array of locking protrusions 4212 are spaced apartto form openings 4213 between adjacent locking protrusions for passingthe second locking protrusions 4214 on the cask body 4101 therethrough,as further described herein.

The longitudinal sides 4203 and lateral ends 4204 of the lid 4200 mayeach include at least one locking bar 4210. In one preferred butnon-limiting embodiment, as illustrated, the lateral ends 4204 of thelid may include a pair of the locking bars 4210 and the longitudinalsides 4203 of the lid may similarly include a pair of locking bars. Thisforms a unique arrangement and interaction between the locking bars tomaintain a locked position, as further described herein.

The corresponding locking features of the bolt-free cask lockingmechanism on cask body 4101 include at least one second locking member4214 a comprising the second locking protrusions 4214. Locking member4214 a may comprise upper portions of cask body 4101 in which the secondlocking protrusions 4214 and related features such as locking slot 4216described below are integrally formed with the cask body inside storagecavity 4105. Locking protrusions 4214 are fixedly disposed in lineararrays on the cask body adjacent to top ends of the longitudinalsidewalls 4103 and lateral end walls 4104 of the body and cask body topopening 4106. The second locking protrusions 4214 are thereforestationary and not movable relative to the cask body. The second lockingprotrusions 4214 project inwardly into the nuclear waste storage cavity4105 from the interior surfaces of the longitudinal sidewalls 4103 andlateral end walls 4104 of the cask body. Second locking protrusions 4214therefore are arranged around the entire perimeter of the cask body tointerface with the first locking protrusions 4212 of lid 4200.

The linear array of second locking protrusions 4214 are spaced apart toform openings 4215 between adjacent locking protrusions for passing thefirst locking protrusions 4212 on the lid therethrough. A linearlyelongated locking slot 4216 is formed and recessed into the cask body4101 immediately below the second locking protrusions 4214 on each ofthe longitudinal sidewalls 4103 and end walls 4104 of the cask body. Thelocking slots 4216 form continuous and uninterrupted inwardly openstructures having a length which extends beneath at least all of thesecond locking protrusions on each of the longitudinal sidewalls 4103and lateral end walls 4104 of the cask body as shown. Locking slots 4216therefore extend for a majority of the lengths/widths of the cask bodylongitudinal sidewalls and end walls. Locking slots 4216 are incommunication with the openings 4215 between the second lockingprotrusions 4214 to form an insertion pathway for the first lockingprotrusions 4212 of lid 4200 to enter the locking slots.

In one preferred but non-limiting construction, the openings 4215between the second locking protrusions 4214 and the elongated lockingslots 4216 may be formed as recesses machined into the cask body 4101 byremoving material from longitudinal sidewalls 4103 and lateral end walls4104. The material remaining therefore leaves the second lockingprotrusions 4214 in relief. Second locking protrusions 4214 therefore inthis case are formed as integral unitary and monolithic parts of thecask body material. In other possible constructions, however, the secondlocking protrusions 4214 may be separate structures which are welded orotherwise fixedly attached to the cask body 4101. In this latterpossible construction, no locking slot 4216 is formed but the casklocking mechanism may nonetheless still function satisfactorily to lockthe lid to the cask body. In yet other possible constructions, thesecond locking protrusions 4214 and locking slots 4216 may be formed onlinearly elongated closure bars of metal having the same compositeconstruction as the longitudinal sidewalls 4103 and end walls 4104previously described herein. The closure bars are in turn welded ontothe tops of each longitudinal sidewalls and end walls to produce thesame structure in the end as illustrated herein.

With continuing reference to FIGS. 70-78 and 82-88 , the first andsecond locking protrusions 4212, 4214 may be generally block-shapedstructures having a rectangular configuration. In one preferred butnon-limiting embodiment, the first and second locking protrusions mayeach be wedge-shaped defining locking wedges having at least one taperedlocking surface 4217 or 4218. The locking protrusions may be configuredand arranged such that the tapered locking surfaces 4217 of the firstlocking protrusions 4212 on lid 4200 are each slideably engageable withone of the tapered locking surfaces 4218 of a corresponding secondlocking protrusion 4214 of the cask body 4101. In one embodiment, thetapered locking surfaces 4217 of the first locking protrusions 4212 onlid 4200 may be formed on a top surface thereof, and the tapered lockingsurfaces 4218 of the second locking protrusions 4214 on cask body 4101may be formed on a bottom surface thereof. When the first and secondlocking protrusions are engaged to lock the lid to the cask body, thetapered locking surfaces 4217, 4218 become slideably engaged forming agenerally flat-to-flat interface therebetween. This creates awedging-action which draws the lid 4200 towards against the cask body4101 to fully compress the gasket 4220 therebetween which forms agas-tight seal of the cask internal storage cavity 4105 and its nuclearwaste material content.

The tapered locking surfaces 4217 and 4218 preferably have the sametaper angle A1 (see, e.g., FIG. 89 ) to form the generally flat-to-flatinterface therebetween when mutually and frictionally engaged via thewedging action. Any suitable taper angle A1 may be used. In onerepresentative but non-limiting examples, the taper angle A1 preferablymay be between about 2 and 20 degrees. Other tapered angles may be usedwhere appropriate.

The locking bars 4210 with first locking protrusions 4212 on lid 4200thereon are slideably, movable between a locked position or state (see,e.g. FIG. 77A) in which the first and second protrusions 4212, 4214 aremutually engaged to prevent removal of the lid 4200 from the cask body4101 (see, e.g. FIG. 71 ), and an unlocked position or state (see, e.g.FIG. 77B) in which the first and second protrusions are disengaged toallow removal of the lid from the cask body in a vertical directiontransverse to longitudinal axis LA of the cask.

To move the locking bars 4210 with sufficient applied force tofrictionally interlock the first and second locking protrusions 4212,4214, and to concomitantly minimize radiation dosage to operatingpersonnel, a remote lid operating system may be provided. This system isoperably coupled to each of the locking bars 4210 and configured toadvantageously move the locking bars 4210 between the locked andunlocked positons from a remote radiation safe distance and area. Thisobviates the need for operators to manually operate the locking barsdirectly at the cask during the lid-to-cask body closure and lockingprocess.

In one embodiment, the remotely-operated lid operating system comprisesa local actuator 4240 mounted on the top surface 4201 of lid 4200 forand coupled to each of the locking bars 4210. FIGS. 87 and 88 showactuators 4240 in isolation and detail. Each actuator 4240 is anassembly which may generally comprise a cylinder-piston assembly 4241including cylinder 4245 and an extendible/retractable piston rod 4242slideably received inside the cylinder. The cylinder-piston assembly isfixedly attached to lid 4200. Cylinder 4245 may be fixedly mounted tothe lid via a bolt 4249 passing through a tubular proximal mounting end4242 b as shown. Pistol rod 4242 has a tubular distal working end 4242 afixedly coupled to the locking bar 4210 through an elongated operatingslot 4243 formed through the lid. The piston rod 4242 is therefore movesthe locking bar 4210 in the manner described herein. In one embodiment,slot 4243 may be formed in a lid insert plate 4243 a which in turn ismounted to the lid. A threaded bolt 4249 may be used to couple thepiston rod to the locking bar 4210 via an intermediate block assemblycomprising an upper mounting block 4246 and lower mounting block 4247.Upper block 4246 may be formed as integral part of lid insert plate 4243a in some embodiments. Piston rod 4242 is fixedly bolted to uppermounting block 4246. Upper mounting block 4246 is fixedly mounted tolower mounting block 4247 via a plurality of threaded fasteners 4248which extend through the upper mounting block and are threadably engagedwith the locking bar 4210 (see, e.g., FIG. 88 ). The mounting blockassembly provides a robust coupling of the piston rods 4242 to thelocking bars 4210 which can withstand the shear forces generated whenthe cylinder-piston assemblies 4241 are actuated to drive the lockingprotrusions 4212, 4214 of the lid 4200 and cask body 4101 into lockingengagement.

The cylinder-piston assembly 4241 may be either (1) hydraulicallyoperated wherein the working fluid is oil, or (2) pneumatically operatedwherein the working fluid is compressed air. Oil or air hoses arefluidly coupled to the cylinder-piston assemblies (not shown) andoperated from a remote hydraulic or pneumatic control unit in aconventional manner which comprises an air compressor or hydraulic pumpwith appropriate valving depending on the type of system provided. Whenactuated, the locking bar actuators 4240 function to slide the lockingbars 4210 between the locked and unlocked positions (FIGS. 77A and 77B)via extending or retracting the piston rod 4242. It bears noting thatthe use of hydraulic or pneumatic means to move the locking bars 4210applies a greater force to the locking bars to form tight lockingengagement via the wedging-action between the first and second lockingprotrusions of the lid and cask body than could be provided by manuallyactuating the locking bars 4210. This advantage, coupled with avoidingexposure of operating personnel or workers to radiation dosage arenotable benefits of the present remote lid operating system.

Interaction between the locking protrusions 4212, 4214 and a relatedprocess/method for locking the nuclear waste cask 4100 (i.e., lid 4200to cask body 4101) are described farther below. The movement andfunctioning of the locking bars 4210, however, is first furtherdescribed.

FIGS. 77A and 77B show the locked and unlocked positions of the lockingbars 4210 on lid 4200. Retention features are provided as a safetymechanism which lock and retain the locking bars in the locked positionto prevent the lid 4200 from being unintentionally unlocked from thecask body 4101, such as could potentially result from substantial forceimpacts occurring during transporting and handling the cask (e.g.,lifting, lowering, or loading the cask onto a transport vehicle/vessel),or during a regulatory postulated cask drop event.

In one embodiment, the locking bars 4210 on the longitudinal sides 4203of lid 4200 are moveable towards each other to form the unlockedposition shown, and away from each other to form the locked positionshown. Conversely, the locking bars 4210 on the lateral ends 4204 of thelid are moveable towards each other to form the locked position, andaway from each other to form the unlocked position. This apparentdichotomy serves a purpose. When locking bars 4210 on the lateral ends4204 of the lid are therefore positioned and abutted together in thelocked position, terminal end portions 4210 a of the locking bars on thelongitudinal sides 4203 of the lid are positioned to overlap andengage/block the locking bars on the lateral ends 4204 of the lid frombeing moved apart to the unlocked position (see, e.g., FIG. 77A). Thisforms a first locking bar retention feature which locks the lid lateralend locking bars 4210 in the locked position.

The second locking bar retention feature acts on the locking bars 4210on the longitudinal sides 4203 of the lid 4200 to lock the lidlongitudinal side locking bars in the locked position. This retentionfeature comprises a locking handle assembly 4230 slideably mounted oneach of the longitudinal sidewalls 4103 of the cask body 4101 (see,e.g., FIGS. 77A-B, 79-81, and 83-86). Each locking handle assembly 4230includes an elongated proximal handle 4231 configured for receiving anapplied force generated by a user such as via grasping or a tool, adistal elongated locking block 4233, and a securement bar 4235. Thelocking block 4233 is coupled to the handle 4231 by one or moreelongated coupling rods 4232 of any suitable polygonal or non-polygonalcross-sectional shape. Preferably a pair of coupling rods 4232 areprovided. Securement bar 4235 is fixedly attached to the exteriorsurface of the cask body longitudinal sidewalls 4103 (e.g., welded) andhas a proximal end 4235 a which is insertable through an aperture 4236in the handle 4231. End 4235 a may project through aperture 4236 whenthe handle assembly is fully inward and can be secured in place (e.g.,FIG. 80 further described herein).

The locking handle assemblies 4230 are positioned on each longitudinalsidewall 4103 of the cask body 4101 to allow the locking block 4233 tobe manually and selectively moved into and out of the locking slots 4216on the cask body sidewalls. A windows 4234 formed in each longitudinalsidewall 4103 allows the locking block 4233 to access the guide channels4216. More particularly, window 4234 is formed in and extends completelythrough inner containment plate 4110 of the longitudinal sidewalls 4103of the cask body. Locking block 4233 is completely retractable fromlocking slot 4216 into the containment plate 4110 to allow insertion offirst locking protrusions 4212 on locking bars 4210 into and slideablymoved along the locking slot 4216 beneath second locking protrusions4214 of the cask body. The outer radiation dose blocker plate 4111comprises a pair of holes 4237 to permit the two coupling rods 4232 tobe coupled to locking block 4233 located inside the blocker plate inwindow 4234 of the inner containment plate 4110 (see, e.g., FIG. 78 ). Apair of cylindrical mounting flange units 4239 may be used to fixedlymount each locking handle assembly 4230 to the dose blocker plate 4111on the longitudinal sidewalls 4103 of cask body 4101 (see, e.g., FIG. 80). Flange units 4239 may be bolted/screwed or welded to the outerblocker plate 4111. The flange units 4239 further act as standoffs tolimit the maximum inward projection of the locking block 4233 into thelocking slot 4216 of the cask body. The coupling rods 4232 are slideablyinward/outward through the flange units to change position of thelocking handle assemblies 4230.

The locking handle assemblies 4230 are moveable via handles 4231 between(1) an inward blocking position in which the locking blocks 4233 projectinto the locking slots 4216 of the cask body 4101 beneath the secondlocking protrusions 4214, and (2) an outward non-blocking position inwhich the locking blocks 4233 are completely retracted from the lockingslots. The non-blocking position allows locking bars 4210 with firstlocking protrusions 4212 thereon to enter and slide back and forth inthe locking slots 4216 between the locked and unlocked positions (bothpreviously described herein) when the lid 4200 is positioned on caskbody 4101. Once the locking bars are in the locked position, a gap G isformed between each pair of locking bars on the longitudinal sides 4203of the lid (see, e.g., FIGS. 72 and 77A). Moving the locking handleassemblies 4230 to the inward blocking position locates the lockingblocks 4233 in and fills the gaps G on each longitudinal sidewall 4103of the cask body (within guide channels 4211 of lid 4200). The lockingbars 4210 therefore cannot be drawn back together to their unlockedposition, thereby locking the locking bars in the locked position due tointerference between the locking blocks 4233 and locking bars. To movethe locking bars 4210 on longitudinal sidewalls 4103 to the unlockedposition, the locking blocks 4233 are first withdrawn via handles 4231of the locking handle assemblies 4230 to re-open gap G, thereby allowingthe longitudinal sidewall locking bars to slide together again to theunlocked position.

When each handle assembly 4230 is in the inward blocking position, thesecurement end 4235 a of securement bar 4235 is projected throughapertures 4236 in handles 4231. Any suitable commercially-availablecable-lock security tag or seal tag 4238 as shown may be coupled throughhole 4235 b in securement bar 4235 to lock the handle assemblies in theinward blocking position. Should the cask 4100 be impacted or droppedduring handled, the lid 4200 will remain locked to the cask body 4101since the handle assemblies 4230 cannot be moved outward to unlock thelid. The security tag also provides visual indication that the lid is inthe locked position to operating personnel. This is especially helpfulin situations where the cask lid 4200 may be loaded with radioactivematerials and locked to the cask body 4101 at one location, and then thecask is transported to a more remote receiving location. The crew at thereceiving location can readily confirm the lid is in the locked positionor state.

A process or method for locking the nuclear waste storage cask 4100using the foregoing features will now be briefly described. FIGS. 89-92are sequential views showing the relationship between the first andsecond locking protrusions 4212, 4214 during the lid mounting and casklocking process.

The process or method generally includes first placing the locking bars4210 on longitudinal sidewalls 4103 and lateral end walls 4104 of lid4200 in their unlocked position and the locking blocks 4233 on lockinghandle assemblies 4230 in their non-blocking positions which retractsthe locking blocks 4233 from the locking slots 4216 on the longitudinalsidewalls 4103 of the cask body 4101 (FIG. 77B). The locking baractuators 4240 or manual means may be used to perform the foregoingstep. The locking bars 4210 on longitudinal sides 4203 of lid 4200 aretogether, and locking bars on lateral ends 4204 of the lid are spacedapart forming gap G therebetween as shown. The lid is positioned overand align with the cask body 4101 wherein the lid first lockingprotrusions 4212 are vertically aligned with the openings 4215 betweensecond locking protrusions 4214 on the cask body (FIG. 89 ).

Next, the closure lid 4200 is lowered and positioned on top of the caskbody 4101 over the top opening 4106. This step first vertically insertsthe peripheral array of first locking protrusions 4212 on locking bars4201 of lid 4200 between the peripheral array of second lockingprotrusions 4214 disposed on the cask body 4101 around the top opening(FIG. 90 ). As the lid engages the top of the cask body 4101, the firstlocking protrusions pass completely through the openings 4215 betweenthe second locking protrusions 4214 and enter the horizontally elongatedlocking slots 4216 in a position below the second locking protrusions(FIG. 91 ). In turn, the second locking protrusions 4214 pass throughopenings 4213 between the first locking protrusions 4212 and becomepositioned above the first locking protrusions.

The process or method continues with then sliding the locking bars 4210to their locked positions (FIGS. 77A and 91 ), which moves the firstlocking protrusions 4212 beneath the second locking protrusions 4214 ina horizontal locking plane oriented parallel to the bottom wall 4102 andpassing through the locking slots 4216. This step may be performed byactuating the hydraulic or pneumatic cylinder-piston assembles 4241 ofthe locking bar actuators 4240 from a location remote from the cask tominimize radiation exposure of operating personnel. Sliding the lockingbars 4210 slideably and frictionally engages the first lockingprotrusions 4212 of the lid with bottom surfaces of the second lockingprotrusions 4214 of the cask body 4101. Specifically, the taperedlocking surfaces 4217, 4218 of the wedge-shaped locking protrusions4212, 4214 become mutually locked in increasingly tightening frictionalengagement via the wedging-action produced. This draws lid 4200 downwardwith added force beyond the weight of the lid alone onto and against thecask body 4101 to fully compress gasket 4220 and seal the cask cavity4105. The gasket is now compressed further than when the lid 4200 firstengages the cask body before the cask locking mechanism is actuated todraw the lid farther downward.

Now that the lid 4200 is fully coupled to the cask body 4101, thelocking handle assemblies 4230 may be moved to their inward blockingpositions to insert the locking blocks 4233 between each pair of lockingbars 4210 on the longitudinal sides 4103 of the lid, thereby preventingsliding and unlocking of the longitudinal side locking bars (FIG. 77A).The handle assemblies therefore retain the locked positions of thelocking bars on the cask longitudinal sidewalls 4103, which in turnretains the locking bars on the cask end walls in the locked position aspreviously described herein.

It bears noting that although the locking bars 4210 with lockingprotrusions 4212 are shown and described herein as being slideablymounted to the lid 4200 and locking protrusions 4214 are shown anddescribed as being fixedly mounted to the cask body 4101 in oneembodiment, in other embodiment the arrangement may be reversed.Accordingly, the locking bars 4210 may be slideably mounted to guidechannels 4211 formed in the cask body while the fixed lockingprotrusions 4214 may instead be fixedly mounted to the closure lid. Thisalternate arrangement provides the same benefits and is operated in thesame manner previously described herein. The locking bar hydraulic orpneumatic actuators 4240 in turn would be mounted to the cask body foroperating the locking bars 4210.

Although the cask locking mechanism with locking bars 4210 and lockingprotrusions 4212, 4214 are shown and described herein as being appliedto a box-shaped rectangular cuboid cask body and rectangular lid, thelocking mechanism may be applied with equal benefit to a conventionalcylindrical cask body and circular lid. The fixed second lockingprotrusions 4214 may be arranged on either the cylindrical cask body orlid, and the locking bars 4210 may be mounted on the other one of thecask body or lid. The locking bars and guide channels for thecylindrical cask application may be arcuately curved and operated viathe hydraulic or pneumatic locking bar actuators 4240 previouslydescribed herein if mounted on either the cask body or circular lid.Alternatively, both the locking protrusions 4212, 4214 may be fixedlymounted to the cylindrical cask body and lid, and the slideable lockingbars may be omitted. In this case, the lid may simply be rotatedrelative to the cylindrical cask body to slideably and frictionallyengage the wedge-shaped locking protrusions to form a breech lock typeclosure. The lid may be rotated via assistance form thehydraulic/pneumatic actuators. Based on the foregoing alternativeembodiments of the cask locking mechanism and description alreadyprovided herein, it is well within the ambit of those skilled in the artto implement any of these options without undue experimentation.

With general reference to FIGS. 61-70 and 81-83 , an impact absorptionsystem is provided to protect the cask 4100 and containment barrier fromundue damage should the cask be forcibly impacted or dropped duringtransport and handling. In one embodiment, each of the longitudinalsidewalls 4103 and lateral end walls 4104 of the cask body 4101comprises a plurality of outwardly protruding impact absorber bars 4140fixedly coupled thereto. The closure lid 4200 and bottom surface 4102 ofthe cask body may also include multiple impact absorber bars 4140fixedly coupled thereto. The bars 4140 may be each configured andarranged in appropriate locations on and in a pattern appropriate tomeet regulatory requirements (e.g., Nuclear Regulator Commission or NRC)for surviving a postulated cask impact/drop event. In one embodiment,the impact absorber bars 4140 may be configured as rectangular blocks ofsuitable thickness and dimension for the intended purpose. The lockinghandle assemblies 4230 on longitudinal sidewalls 4103 of cask body 4101may each be protected between at least a pair of absorber bars 4140located proximately to the assembly on each side. These protectiveimpact absorber bars have depth measured perpendicularly to the exteriorsurface of the cask body longitudinal sidewalk 4103 such that the handleassemblies 4230 do not protrude outwards beyond the bars. In oneembodiment, the impact absorber bars 4140 may be bolted to the cask bodyand lid (see, e.g., FIGS. 83-86 ). This allows the bars to be readilyreplaced if damaged during a cask drop/impact event. In otherembodiments, the bars 4140 maybe welded thereto.

Each corner 4107 of the cask body 4101 and corners 4205 of lid 4200 maybe protected by corner impact absorbers 4141 fixedly coupled to cornerregions. Sets of upper and lower corner impact absorber are provided tocover and shield the lid and adjacent upper corner regions of the caskbody, and the bottom wall 4102 and adjacent lower corner regions of thecask body, respectively. In one embodiment, the corner impact absorbers4141 may be assemblies comprising an inner corner bracket 4142 and outercorner blocks 4143 fixedly coupled thereto. Inner corner brackets 4142may be fixedly coupled to the cask body 4101 at the lower corners of thebody, and the lid and/or cask body at the upper corners. In oneembodiment, the inner corner brackets 4142 and corner blocks 4143 may befixedly coupled to and movable with lid 4200 as shown herein. The innercorner brackets 4142 have inward facing concave recesses configured toconform to the perpendicular and squared off corners of the cask bodyand lid. The outer corner blocks 4143 have concave recesses configuredto conform to the exterior shape of the inner corner brackets 4142. Theupper corner impact absorbers 4141 extend vertically downwards from thelid over the upper corners of the cask body, and horizontally wraplongitudinally and laterally around the side regions of the corners onboth the cask body 4101 and lid 4200. The upper corner impact absorbersalso extend partially over the top of the lid at the corners. The lowercorner impact absorbers 4141 horizontally wrap longitudinal andlaterally around the side regions of the corners on the cask body 4101and bottom wall 4102, and partially underneath the bottom wall. In oneembodiment, the inner corner brackets 4142 and outer corner blocks 4143may be bolted or screwed together via threaded fasteners. The innercorner brackets 4142 may in turn be bolted or screws to the cask body4101 and cask body and/or lid 4200 vi threaded fasteners as applicable.

To facilitate handling the cask 4100, each of the longitudinal sidewalls4103 of cask body 4101 may include a plurality of outwardly protrudinglifting trunnions 4150 fixedly attached thereto. Lifting trunnions 4150may be generally cylindrical in configuration and of the retractabletype in one embodiment which are known in the art. The lid 4200 in turnmay include a plurality of lifting lugs 4151 for handling the lid. Lugs4151 are fixedly attached to the lid. Lifting lugs may be generallycylindrical in configuration in one embodiment. Any suitable number oflifting trunnions and lugs may be provided as needed to safely lift andmaneuver the cask body and lid. Other configurations and constructionsof the lifting trunnions and lugs may be provided which are suitable forlifting and maneuvering the weight of cask body and lid in a stablemanner.

While the foregoing description and drawings represent some examplesystems, it will be understood that various additions, modifications andsubstitutions may be made therein without departing from the spirit andscope and range of equivalents of the accompanying claims. Inparticular, it will be clear to those skilled in the art that thepresent invention may be embodied in other forms, structures,arrangements, proportions, sizes, and with other elements, materials,and components, without departing from the spirit or essentialcharacteristics thereof. In addition, numerous variations in themethods/processes described herein may be made. One skilled in the artwill further appreciate that the invention may be used with manymodifications of structure, arrangement, proportions, sizes, materials,and components and otherwise, used in the practice of the invention,which are particularly adapted to specific environments and operativerequirements without departing from the principles of the presentinvention. The presently disclosed embodiments are therefore to beconsidered in all respects as illustrative and not restrictive, thescope of the invention being defined by the appended claims andequivalents thereof, and not limited to the foregoing description orembodiments. Rather, the appended claims should be construed broadly, toinclude other variants and embodiments of the invention, which may bemade by those skilled in the art without departing from the scope andrange of equivalents of the invention.

What is claimed is:
 1. A nuclear waste cask with impact protectioncomprising: a longitudinal axis; a longitudinally elongated cask bodyincluding a top end, a bottom end, and a sidewall extending between theends, and a cavity configured for holding a nuclear waste canister; andan impact limiter coupled to the top end of the cask body, the impactlimiter comprising an annular perforated sleeve having a body includinga central opening and a circumferential array of elongated longitudinalpassages formed therethrough around the central opening.
 2. The caskaccording to claim 1, wherein the longitudinal passages are orientedparallel to each other and extend between a top surface and a bottomsurface of the perforated sleeve.
 3. The cask according to claim 2,wherein the longitudinal passages are oriented parallel to thelongitudinal axis of the cask.
 4. The cask according to claim 2, whereinthe longitudinal passages have a circular transverse cross section. 5.The cask according to claim 4, wherein the longitudinal passages eachhave a longitudinal length which is greater than their respectivediameter.
 6. A method for ameliorating impact between components of afuel storage system, the method comprising: partially embedding aplurality of impact limiter plugs in corresponding plug holes formed ina bottom closure plate of a cask; seating the canister on the plugs, theplugs being positioned at a first depth in the plug holes; impacting thecanister against the plugs with an impact force; and driving the plugsto a second depth in the plug holes deeper than the first depth.
 7. Themethod according to claim 6, wherein pact force in the impacting step isa result of dropping the cask against a surface.
 8. The method accordingto claim 6, wherein the driving step includes frictionally engaging andsliding tapered sides of the plugs along tapered sidewalls of the plugholes.
 9. The method according to claim 6, wherein the seating stepincludes engaging the plugs with a bottom baseplate of the canister. 10.The method according to claim herein the plugs have a frustoconicalshape and at least a portion of the plug holes have a frustoconicalshape.
 11. A method for protecting an unventilated nuclear waste storagesystem from internal overpressurization, the method comprising:providing an unventilated cask comprising a sealable internal cavity anda plurality of threaded anchor bosses; lowering a canister containinghigh level nuclear waste into the cavity; positioning a radiationshielded lid on the cask, the lid being in a downward sealed positionengaged with the cask making the cavity gas tight to retain pressuresexceeding atmospheric; aligning a plurality of fastener holes formed inthe lid with the anchor bosses; threadably engaging a threaded stud witheach of the anchor bosses through the fastener holes of the lid;rotatably engaging a threaded limit stop with each of the threadedstuds; positioning the limits stops on the studs such that a verticaltravel gap is formed between the lid and the limit stops; wherein duringa cask overpressurization condition, the lid slideably moves upwardalong the studs to a relief position ajar from the cask to vent excesspressure to atmosphere.
 12. The method according to claim 11, whereinwhen the cask overpressurization condition abates, the lid automaticallyreturning to the downward sealed position to re-engage the cask body andreseal the cavity.
 13. The method according to claim 11, furthercomprising pumping air out of the cavity of the cask after positioningthe lid on the cask to establish a sub-atmospheric pressure in thecavity.
 14. The method according to claim 13, further comprising fillingthe cavity of the cask with an inert gas.
 15. A method for locking aradioactive waste storage cask comprising: positioning a closure lid ona cask body over an opening leading into an internal storage cavity;inserting a peripheral array of first locking protrusions on the lidbetween and through a peripheral array of second locking protrusionsdisposed on the cask body around the opening; slideably moving the firstlocking protrusions beneath the second locking protrusions; andfrictionally engaging the first locking protrusions with the secondlocking protrusions; wherein the lid cannot be removed from the caskbody.
 16. The method according to claim 15, wherein when the firstlocking protrusions are arranged in spaced apart groups on a pluralityof locking bars slideably mounted on the lid, the locking bars beingslideably movable relative to the lid.
 17. The method according to claim16, wherein the slideably moving step comprises sliding each of thelocking bars from an unlocked position in which the first lockingprotrusions do not engage the second locking protrusions, to a lockedposition in which the first locking protrusions are positioned beneaththe second locking protrusions.
 18. The method according to claim 15,wherein the frictionally engaging step comprises engaging a taperedlocking surface on each of the first locking protrusions with acorresponding tapered locking surface on a respective one of the secondlocking protrusions which locks the lid to the cask body via a wedgingaction.
 19. The method according to claim 18, wherein engaging thetapered locking surfaces of the first and second locking protrusionsdraws the lid against the cask body in tightened engagement.
 20. Themethod according to claim 19, further comprising compressing a gasketbetween the lid and the cask body when the lid is drawn against the caskbody.